10-Q

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-Q

(Mark one)

þ QUARTERLY REPORT PURSUANT TO SECTION 13 or 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the Quarterly Period Ended March 31, 2013

or

o Transition Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934.

For the Transition Period from to .

Commission File Number 1-15202

W. R. BERKLEY CORPORATION

(Exact name of registrant as specified in its charter)

Delaware	22-1867895
(State or other jurisdiction of	(I.R.S. Employer
incorporation or organization)	Identification No.)
475 Steamboat Road, Greenwich, Connecticut	06830
(Address of principal executive offices)	(Zip Code)

	(203) 629-3000
	(Registrant’s telephone number, including area code)
	None
Former name, former address and former fiscal year, if changed since last report.

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes þ     No o

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yes þ     No o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer,” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer þ	Accelerated filer o	Non-accelerated filer o	Smaller reporting company o
		(Do not check if a smaller reporting company)

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes o     No þ

Number of shares of common stock, $.20 par value, outstanding as of April 30, 2013: 136,036,887

TABLE OF CONTENTS

Part I — FINANCIAL INFORMATION
	Item 1. Financial Statements
	Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations
	Item 3. Quantitative and Qualitative Disclosure About Market Risk
	Item 4. Controls and Procedures
PART II — OTHER INFORMATION
	Item 1. Legal Proceedings
	Item 1A. Risk Factors
	Item 2. Unregistered Sales of Equity Securities and Use of Proceeds
	Item 6. Exhibits
SIGNATURES
EX-31.1
EX-31.2
EX-32.1
EX-101 INSTANCE DOCUMENT
EX-101 SCHEMA DOCUMENT
EX-101 CALCULATION LINKBASE DOCUMENT
EX-101 LABELS LINKBASE DOCUMENT
EX-101 PRESENTATION LINKBASE DOCUMENT
EX-101 DEFINITION LINKBASE DOCUMENT

Part I — FINANCIAL INFORMATION

Item 1. Financial Statements

W. R. BERKLEY CORPORATION AND SUBSIDIARIES

CONSOLIDATED BALANCE SHEETS

(Dollars in thousands)

	March 31, 2013			December 31, 2012
	(Unaudited)
Assets
Investments:
Fixed maturity securities	$	11,665,117		$	11,943,956
Equity securities	399,386			376,022
Arbitrage trading account	701,223			329,077
Investment funds	793,603			809,689
Loans receivable	456,533			401,961
Real estate	588,777			606,735
Total investments	14,604,639			14,467,440
Cash and cash equivalents	945,492			905,670
Premiums and fees receivable	1,504,535			1,440,752
Due from reinsurers	1,441,389			1,450,348
Accrued investment income	126,577			127,230
Prepaid reinsurance premiums	345,329			316,309
Deferred policy acquisition costs	425,070			404,047
Real estate, furniture and equipment	271,012			267,227
Goodwill	107,529			87,865
Trading account receivables from brokers and clearing organizations	28,720			446,873
Other assets	320,342			242,135
Total assets	$	20,120,634		$	20,155,896
Liabilities and Equity
Liabilities:
Reserves for losses and loss expenses	$	9,809,843		$	9,751,086
Unearned premiums	2,635,995			2,474,847
Due to reinsurers	298,557			316,388
Trading account securities sold but not yet purchased	79,965			121,487
Federal and foreign income taxes - current and deferred	104,810			82,801
Other liabilities	844,297			959,080
Junior subordinated debentures	243,258			243,206
Senior notes and other debt	1,693,279			1,871,535
Total liabilities	15,710,004			15,820,430
Equity:
Preferred stock, par value $.10 per share:
Authorized 5,000,000 shares; issued and outstanding - none	—			—
Common stock, par value $.20 per share:
Authorized 500,000,000 shares, issued and outstanding, net of treasury shares, 136,028,287 and 136,017,732 shares, respectively	47,024			47,024
Additional paid-in capital	949,926			945,166
Retained earnings	4,922,178			4,817,807
Accumulated other comprehensive income	428,592			465,631
Treasury stock, at cost, 99,089,631and 99,100,186 shares, respectively	(1,969,179		)	(1,969,411		)
Total stockholders’ equity	4,378,541			4,306,217
Noncontrolling interests	32,089			29,249
Total equity	4,410,630			4,335,466
Total liabilities and equity	$	20,120,634		$	20,155,896

See accompanying notes to interim consolidated financial statements.

1

W. R. BERKLEY CORPORATION AND SUBSIDIARIES

CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED)

(Dollars in thousands, except per share data)

	For the Three Months Ended
	March 31
	2013			2012
REVENUES:
Net premiums written	$	1,376,966		$	1,203,526
Change in net unearned premiums	(144,847		)	(103,875		)
Net premiums earned	1,232,119			1,099,651
Net investment income	135,929			157,619
Insurance service fees	26,736			23,877
Net investment gains	19,969			43,477
Change in valuation allowance, net of other-than-temporary impairments	—			4,014
Revenues from wholly-owned investees	91,735			49,675
Other income	281			392
Total revenues	1,506,769			1,378,705
OPERATING COSTS AND EXPENSES:
Losses and loss expenses	744,679			679,472
Other operating costs and expenses	481,604			431,779
Expenses from wholly-owned investees	89,152			51,330
Interest expense	31,111			28,821
Total operating costs and expenses	1,346,546			1,191,402
Income before income taxes	160,223			187,303
Income tax expense	(43,625		)	(52,071		)
Net income before noncontrolling interests	116,598			135,232
Noncontrolling interests	17			86
Net income to common stockholders	$	116,615		$	135,318
NET INCOME PER SHARE:
Basic	$	0.86		$	0.98
Diluted	0.83			0.94

See accompanying notes to interim consolidated financial statements.

2

W. R. BERKLEY CORPORATION AND SUBSIDIARIES

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED)

(Dollars in thousands)

	For the Three Months Ended
	March 31
	2013			2012
Net income before noncontrolling interests	$	116,598		$	135,232
Other comprehensive income (loss):
Change in unrealized translation adjustments	(46,623		)	15,583
Change in unrealized investment gains (losses), net of taxes	7,810			22,024
Change in net pension asset, net of taxes	1,814			824
Other comprehensive income (loss)	(36,999		)	38,431
Comprehensive income	79,599			173,663
Comprehensive (income) loss to the noncontrolling interest	(23		)	63
Comprehensive income to common stockholders	$	79,576		$	173,726

See accompanying notes to interim consolidated financial statements.

3

W. R. BERKLEY CORPORATION AND SUBSIDIARIES

CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY (UNAUDITED)

(Dollars in thousands)

	For the Three Months Ended
	March 31
	2013			2012
COMMON STOCK:
Beginning and end of period	$	47,024		$	47,024
ADDITIONAL PAID-IN CAPITAL:
Beginning of period	$	945,166		$	941,109
Stock options exercised and restricted stock units issued, net of tax	(233		)	(10,139		)
Restricted stock units expensed	4,993			7,447
End of period	$	949,926		$	938,417
RETAINED EARNINGS:
Beginning of period	$	4,817,807		$	4,491,162
Net income to common stockholders	116,615			135,318
Dividends	(12,244		)	(11,041		)
End of period	$	4,922,178		$	4,615,439
ACCUMULATED OTHER COMPREHENSIVE INCOME:
Unrealized investment gains:
Beginning of period	$	517,658		$	430,419
Unrealized gains on securities not other-than-temporarily impaired	7,047			20,868
Unrealized gains on other-than-temporarily impaired securities	723			1,133
End of period	525,428			452,420
Currency translation adjustments:
Beginning of period	(36,676		)	(61,239		)
Net change in period	(46,623		)	15,583
End of period	(83,299		)	(45,656		)
Net pension asset:
Beginning of period	(15,351		)	(14,329		)
Net change in period	1,814			824
End of period	(13,537		)	(13,505		)
Total accumulated other comprehensive income	$	428,592		$	393,259
TREASURY STOCK:
Beginning of period	$	(1,969,411	)	$	(1,880,790	)
Stock exercised/vested	232			20,099
Stock repurchased	—			(6,532		)
End of period	$	(1,969,179	)	$	(1,867,223	)
NONCONTROLLING INTERESTS:
Beginning of period	$	29,249		$	7,526
Contributions	2,817			1,076
Net income	(17		)	(86		)
Other comprehensive income, net of tax	40			23
End of period	$	32,089		$	8,539

See accompanying notes to interim consolidated financial statements.

4

W. R. BERKLEY CORPORATION AND SUBSIDIARIES

CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED)

(Dollars in thousands)

	For the Three Months Ended
	March 31,
	2013			2012
CASH FROM OPERATING ACTIVITIES:
Net income to common stockholders	$	116,615		$	135,318
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	(19,969		)	(47,491		)
Depreciation and amortization	20,910			22,212
Noncontrolling interests	(17		)	(86		)
Investment funds	(10,934		)	(27,624		)
Stock incentive plans	4,989			7,447
Change in:
Arbitrage trading account	4,485			(2,946		)
Premiums and fees receivable	(76,268		)	(97,077		)
Reinsurance accounts	(34,039		)	(16,857		)
Deferred policy acquisition costs	(23,608		)	(11,483		)
Income taxes	22,471			48,160
Reserves for losses and loss expenses	84,569			47,443
Unearned premiums	174,229			115,434
Other	(148,321		)	(98,688		)
Net cash from operating activities	115,112			73,762
CASH FROM (USED IN) INVESTING ACTIVITIES:
Proceeds from sale of fixed maturity securities	463,388			295,134
Proceeds from sale of equity securities	38,248			32,575
Distributions from (contributions to) investment funds	(22,072		)	24,744
Proceeds from maturities and prepayments of fixed maturity securities	667,711			408,647
Purchase of fixed maturity securities	(896,378		)	(872,588		)
Purchase of equity securities	(35,486		)	(68,652		)
Real estate purchased	(10,301		)	(5,611		)
Change in loans receivable	(53,405		)	(93,934		)
Net additions to real estate, furniture and equipment	(13,042		)	(15,055		)
Change in balances due to security brokers	43,325			16,146
Payment for business purchased, net of cash acquired	(38,556		)	—
Net cash from (used in) investing activities	143,432			(278,594		)
CASH FROM (USED IN) FINANCING ACTIVITIES:
Repayment of senior notes and other debt	(206,280		)	(1,684		)
Net proceeds from issuance of debt	—			354,315
Net proceeds from stock options exercised	—			3,428
Other, net	7,638			10,446
Net cash from (used in) financing activities	(198,642		)	366,505
Net impact on cash due to change in foreign exchange rates	(20,080		)	8,992
Net change in cash and cash equivalents	39,822			170,665
Cash and cash equivalents at beginning of year	905,670			911,742
Cash and cash equivalents at end of period	$	945,492		$	1,082,407

See accompanying notes to interim consolidated financial statements.

5

W. R. Berkley Corporation and Subsidiaries

NOTES TO INTERIM CONSOLIDATED FINANCIAL STATEMENTS (UNAUDITED)

(1) General

The accompanying unaudited consolidated financial statements of W. R. Berkley Corporation and its subsidiaries (the “Company”) have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information. Accordingly, they do not include all the information and notes required by GAAP for annual financial statements. The unaudited consolidated financial statements reflect all adjustments, consisting only of normal recurring items, which are necessary to present fairly the Company’s financial position and results of operations on a basis consistent with the prior audited consolidated financial statements. Operating results for interim periods are not necessarily indicative of the results that may be expected for the year. All significant intercompany accounts and transactions have been eliminated. The preparation of financial statements requires the use of management estimates. For further information related to a description of areas of judgment and estimates and other information necessary to understand the Company’s financial position and results of operations, refer to the audited consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012. Reclassifications have been made in the 2012 financial statements as originally reported to conform to the presentation of the 2013 financial statements.

The income tax provision has been computed based on the Company’s estimated annual effective tax rate. The effective tax rate for the quarter differs from the federal income tax rate of 35% principally because of tax-exempt investment income.

(2) Per Share Data

The Company presents both basic and diluted net income per share (“EPS”) amounts. Basic EPS is calculated by dividing net income by the weighted average number of common shares outstanding during the period. Diluted EPS is based upon the weighted average number of common and common equivalent shares outstanding during the period and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect. Stock options for which the exercise price exceeds the average market price over the period have an anti-dilutive effect on EPS and, accordingly, are excluded from the calculation.

The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows:

(In thousands)	For the Three Months Ended
	March 31,
	2013	2012
Basic	136,025	137,814
Diluted	141,223	143,411

(3) Recent Accounting Pronouncements

In February 2013, the Financial Accounting Standards Board (FASB) issued ASU 2013-02 relating to disclosures about items reclassified out of accumulated other comprehensive income. The Company’s adoption of the updated guidance effective January 1, 2013 resulted in a change in the disclosures for accumulated other comprehensive income in the Company’s consolidated financial statements but did not have any impact on the Company’s results of operations, financial position or liquidity.

All recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.

(4) Acquisitions

In 2012, the Company acquired a 49% interest in a worldwide supplier of after-market original equipment manufacturer (OEM) parts, systems and custom logistic support services for military aircraft operations for $43 million. In January 2013, the Company acquired the remaining 51% of this business for $43 million. The estimated useful lives of the intangible assets acquired range from 2 years to 15 years, with approximately $3 million having an indefinite life.

6

The following table summarizes the estimated fair value of net assets acquired and liabilities assumed at the date of acquisition:

(In thousands)	Acquired in 2013
Cash and cash equivalents	$	3,911
Real estate, furniture and equipment	898
Goodwill	19,664
Intangible assets	44,800
Other assets	60,661
Total assets acquired	129,934
Debt	(27,612		)
Other liabilities assumed	(17,076		)
Net assets acquired	$	85,246

(5) Statement of Comprehensive Income (Loss)

The following table presents the components of the changes in accumulated other comprehensive income (loss) (AOCI) as of and for the three months ended March 31, 2013:

	Unrealized Investment gains					Currency translation adjustments			Net pension asset					Accumulated other comprehensive income (loss)
(In thousands)
Changes in AOCI
Beginning of period	$	517,658				$	(36,676	)	$	(15,351	)			$	465,631
Other comprehensive income (loss) before reclassifications	20,989					(46,623		)	—					(25,634		)
Amounts reclassified from AOCI	(13,179		)			—			1,814					(11,365		)
Other comprehensive income (loss)	7,810					(46,623		)	1,814					(36,999		)
Unrealized investment gain related to non-controlling interest	(40		)			—			—					(40		)
Ending balance	$	525,428				$	(83,299	)	$	(13,537	)			$	428,592
Amounts reclassified from AOCI
Pre-tax	$	(20,075	)	(1	)	$	—		$	2,792		(3	)	$	(17,283	)
Tax effect	6,896			(2	)	—			(978		)	(2	)	5,918
After-tax amounts reclassified	$	(13,179	)			$	—		$	1,814				$	(11,365	)
Other comprehensive income (loss)
Pre-tax	$	12,015				$	(46,623	)	$	2,792				$	(31,816	)
Tax effect	(4,205		)			—			(978		)			(5,183		)
Other comprehensive income (loss)	$	7,810				$	(46,623	)	$	1,814				$	(36,999	)

_______________

(1) Net investment gains in the consolidated statements of operations.

(2) Income tax expense in the consolidated statements of operations.

(3) Other operating costs and expenses in the consolidated statements of operations.

(6) Statements of Cash Flow

Interest payments were $53,691,000 and $45,358,000 and income taxes paid were $23,850,000 and $3,249,000 in the three months ended March 31, 2013 and 2012, respectively.

7

(7) Investments in Fixed Maturity Securities

At March 31, 2013 and December 31, 2012, investments in fixed maturity securities were as follows:

(In thousands)	Amortized Cost		Gross Unrealized					Fair Value		Carrying Value
			Gains		Losses
March 31, 2013
Held to maturity:
State and municipal	$	66,125	$	17,675	$	—		$	83,800	$	66,125
Residential mortgage-backed	31,181		4,977		—			36,158		31,181
Corporate	4,997		555		—			5,552		4,997
Total held to maturity	102,303		23,207		—			125,510		102,303
Available for sale:
U.S. government and government agency	807,341		68,429		(58		)	875,712		875,712
State and municipal	4,110,714		308,121		(9,219		)	4,409,616		4,409,616
Mortgage-backed securities:
Residential (1)	1,293,875		48,550		(6,878		)	1,335,547		1,335,547
Commercial	203,260		6,504		(398		)	209,366		209,366
Corporate	3,370,627		210,832		(10,380		)	3,571,079		3,571,079
Foreign	1,065,472		96,381		(359		)	1,161,494		1,161,494
Total available for sale	10,851,289		738,817		(27,292		)	11,562,814		11,562,814
Total investments in fixed maturity securities	$	10,953,592	$	762,024	$	(27,292	)	$	11,688,324	$	11,665,117
December 31, 2012
Held to maturity:
State and municipal	$	65,190	$	18,529	$	—		$	83,719	$	65,190
Residential mortgage-backed	32,764		5,286		—			38,050		32,764
Corporate	4,997		605		—			5,602		4,997
Total held to maturity	102,951		24,420		—			127,371		102,951
Available for sale:
U.S. government and government agency	827,591		72,532		(1,660		)	898,463		898,463
State and municipal	4,449,238		328,974		(9,693		)	4,768,519		4,768,519
Mortgage-backed securities:
Residential (1)	1,395,739		53,846		(7,456		)	1,442,129		1,442,129
Commercial	268,671		5,641		(744		)	273,568		273,568
Corporate	3,144,480		214,322		(12,083		)	3,346,719		3,346,719
Foreign	1,029,284		83,347		(1,024		)	1,111,607		1,111,607
Total available for sale	11,115,003		758,662		(32,660		)	11,841,005		11,841,005
Total investments in fixed maturity securities	$	11,217,954	$	783,082	$	(32,660	)	$	11,968,376	$	11,943,956

___________

(1) Gross unrealized losses for residential mortgage-backed securities include $1,925,000 and $3,037,000 as of March 31, 2013 and December 31, 2012, respectively, related to the non-credit portion of other-than-temporary impairments (“OTTI”) recognized in other comprehensive income.

8

The amortized cost and fair value of fixed maturity securities at March 31, 2013, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations.

(In thousands)	Amortized Cost		Fair Value
Due in one year or less	$	798,683	$	826,292
Due after one year through five years	3,482,465		3,673,747
Due after five years through ten years	2,536,987		2,806,448
Due after ten years	2,607,141		2,800,766
Mortgage-backed securities	1,528,316		1,581,071
Total	$	10,953,592	$	11,688,324

At March 31, 2013, there were no investments, other than investments in United States government and government agency securities, which exceeded 10% of common stockholders’ equity.

(8) Investments in Equity Securities

At March 31, 2013 and December 31, 2012, investments in equity securities were as follows:

(In thousands)	Cost		Gross Unrealized					Fair Value		Carrying Value
			Gains		Losses
March 31, 2013
Common stocks	$	224,378	$	71,995	$	(1,342	)	$	295,031	$	295,031
Preferred stocks	82,600		23,340		(1,585		)	104,355		104,355
Total	$	306,978	$	95,335	$	(2,927	)	$	399,386	$	399,386
December 31, 2012
Common stocks	$	222,671	$	60,102	$	(707	)	$	282,066	$	282,066
Preferred stocks	85,504		10,103		(1,651		)	93,956		93,956
Total	$	308,175	$	70,205	$	(2,358	)	$	376,022	$	376,022

(9) Arbitrage Trading Account

At March 31, 2013 and December 31, 2012, the fair value and carrying value of the arbitrage trading account were $701 million and $329 million, respectively. The primary focus of the trading account is merger arbitrage. Merger arbitrage is the business of investing in the securities of publicly held companies which are the targets in announced tender offers and mergers. Arbitrage investing differs from other types of investing in its focus on transactions and events believed likely to bring about a change in value over a relatively short time period (usually four months or less). The Company believes that this makes arbitrage investments less vulnerable to changes in general financial market conditions.

9

(10) Net Investment Income

Net investment income consists of the following:

	For the Three Months Ended
	March 31,
(In thousands)	2013			2012
Investment income earned on:
Fixed maturity securities, including cash and cash equivalents and loans receivable	$	117,836		$	119,288
Investment funds	10,934			27,623
Arbitrage trading account	3,783			6,481
Equity securities available for sale	2,247			3,150
Real estate	3,141			2,176
Gross investment income	137,941			158,718
Investment expense	(2,012		)	(1,099		)
Net investment income	$	135,929		$	157,619

(11) Investment Funds

Investment funds consist of the following:

	Carrying Value as of				Income (Losses) from Investment Funds
	March 31		December 31,		For the Three Months Ended March 31,
(In thousands)	2013		2012		2013			2012
Real estate	$	379,006	$	373,259	$	(2,001	)	$	8,655
Energy	147,383		146,325		9,466			17,938
Arbitrage	63,462		63,920		(458		)	1,770
Other	203,752		226,185		3,927			(740		)
Total	$	793,603	$	809,689	$	10,934		$	27,623

The Company's share of the earnings or losses of investment funds is generally reported on a one-quarter lag in order to facilitate the timely completion of the Company's consolidated financial statements.

(12) Real Estate

Investment in real estate represents directly owned property held for investment, as follows:    

	Carrying value as of
	March 31,		December 31,
(In thousands)	2013		2012
Properties in operation	$	264,755	$	282,899
Properties under development	324,022		323,836
Total	$	588,777	$	606,735

Properties in operation represent an office building in London and a long-term ground lease in Washington D.C. These properties are net of accumulated depreciation and amortization of $11,397,000 and $10,354,000, as of March 31, 2013 and December 31, 2012, respectively. Related depreciation expense was $1,757,000 and $2,105,000 for the three months ended March 31, 2013 and 2012, respectively. Future minimum rental income expected on operating leases relating to real estate held for investment is $1,099,000 in 2013, $1,504,000 in 2014, $1,549,000 in 2015, $1,596,000 in 2016, $1,644,000 in 2017 and $329,013,000 thereafter.

Properties under development represent an office building in London, a mixed-use project in Washington D.C. and an office complex in New York City. The Company expects to fund further development costs for these projects with a combination of its own funds and external financing.

10

(13) Loans Receivable

Loans receivable are as follows:

(In thousands)	March 31, 2013		December 31, 2012
Loans receivable	$	456,533	$	401,961
Valuation allowance:
Specific	$	3,500	$	3,000
General	2,682		2,620
Total	$	6,182	$	5,620
Impaired loans:
With a specific valuation allowance	$	3,003	$	1,775
Without a valuation allowance	30,000		31,023
Unpaid principal balance	36,003		35,872
	For the Three Months Ended March 31,
	2013		2012
Increase (decrease) in valuation allowance	$	62	$	(6,896	)
Loans receivable charged off	463		85

Loans receivable in non-accrual status were $3 million at both March 31, 2013 and December 31, 2012. If these loans had been current, additional interest income of $0.7 million and $0.2 million would have been recognized in accordance with their original terms for the three months ended March 31, 2013 and 2012, respectively.

The Company monitors the performance of its loans receivable and assesses the ability of the borrower to pay principal and interest based upon loan structure, underlying property values, cash flow and related financial and operating performance of the property and market conditions. Loans receivable with a potential for default are further assessed using discounted cash flow analysis and comparable cost and sales methodologies, if appropriate.

The Company's six largest loans receivable, which have an aggregate amortized cost of $243 million and an aggregate fair value of $250 million at March 31, 2013, are secured by commercial real estate located primarily in New York City, California, Hawaii and Chicago. These loans earn interest at floating LIBOR-based interest rates and have maturities (inclusive of extension options) through August 2025.

The Company utilizes an internal risk rating system to assign a risk to each of its commercial loans. The loan rating system takes into consideration credit quality indicators including loan to value ratios, which compare the outstanding loan amount to the estimated value of the property, the borrower's financial condition and performance with respect to loan terms, the Company's position in the capital structure, and the overall leverage in the capital structure. Based on this rating system, one loan with an aggregate cost basis of $30 million was considered to be impaired at March 31, 2013. A determination was made as to the amount of loss in the event of a default and whether the loss is probable. The results of the determination were considered in connection with the valuation allowance noted above.

11

(14) Realized and Unrealized Investment Gains

Realized and unrealized investment gains and losses are as follows:

	For the Three Months Ended March 31,
(In thousands)	2013			2012
Realized investment gains and losses:
Fixed maturity securities:
Gains	$	10,996		$	14,955
Losses	(5,966		)	(543		)
Equity securities available for sale	15,245			26,238
Investment funds	194			1,310
Other	(500		)	1,517
Total	19,969			43,477
Change in valuation allowance, net other-than-temporary impairments:
Decrease in valuation allowance	—			6,998
Other-than-temporary impairments	—			(2,984		)
Total	—			4,014
Net investment gains	19,969			47,491
Income tax expense	(6,989		)	(16,409		)
Total after-tax investment gains and losses	$	12,980		$	31,082

Change in unrealized investment gains and losses:
Fixed maturity securities	$	(15,589	)	$	19,422
Previously impaired fixed maturity securities	1,112			1,743
Equity securities available for sale	24,561			11,595
Investment funds	(3,268		)	1,677
Total change in unrealized investment gains and losses	6,816			34,437
Income tax benefit (expense)	994			(12,413		)
Noncontrolling interests	(40		)	(23		)
Total after-tax unrealized gains and losses	$	7,770		$	22,001

12

(15) Securities in an Unrealized Loss Position

The following table summarizes all securities in an unrealized loss position at March 31, 2013 and December 31, 2012 by the length of time those securities have been continuously in an unrealized loss position:

	Less Than 12 Months				12 Months or Greater				Total
(In thousands)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
March 31, 2013
U.S. government and agency	$	24,203	$	58	$	—	$	—	$	24,203	$	58
State and municipal	133,592		1,830		100,664		7,389		234,256		9,219
Mortgage-backed securities	451,452		4,235		44,419		3,041		495,871		7,276
Corporate	348,050		2,425		66,309		7,955		414,359		10,380
Foreign	91,803		309		3,221		50		95,024		359
Fixed maturity securities	1,049,100		8,857		214,613		18,435		1,263,713		27,292
Common stocks	31,119		1,342		—		—		31,119		1,342
Preferred stocks	386		235		24,324		1,350		24,710		1,585
Equity securities	31,505		1,577		24,324		1,350		55,829		2,927
Total	$	1,080,605	$	10,434	$	238,937	$	19,785	$	1,319,542	$	30,219
December 31, 2012
U.S. government and agency	$	69,551	$	1,660	$	—	$	—	$	69,551	$	1,660
State and municipal	152,694		1,639		135,967		8,054		288,661		9,693
Mortgage-backed securities	484,731		3,629		58,292		4,571		543,023		8,200
Corporate	371,781		2,964		70,537		9,119		442,318		12,083
Foreign	95,623		996		11,210		28		106,833		1,024
Fixed maturity securities	1,174,380		10,888		276,006		21,772		1,450,386		32,660
Common stocks	46,725		707		—		—		46,725		707
Preferred stocks	—		—		39,812		1,651		39,812		1,651
Equity securities	46,725		707		39,812		1,651		86,537		2,358
Total	$	1,221,105	$	11,595	$	315,818	$	23,423	$	1,536,923	$	35,018

Fixed Maturity Securities – A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2013 is presented in the table below.

($ in thousands)	Number of Securities	Aggregate Fair Value			Gross Unrealized Loss
Unrealized loss greater than $5 million:	—	$	—	—	$	—
Unrealized loss less than $5 million:
Mortgage-backed securities	12	54,367			2,925
Corporate	9	28,242			3,172
State and municipal	2	24,654			1,264
Foreign	1	11,513			7
Total	24	$	118,776		$	7,368

For OTTI of fixed maturity securities that management does not intend to sell or, more likely than not, would not be required to sell, the portion of the decline in value considered to be due to credit factors is recognized in earnings and the portion of the decline in value considered to be due to non-credit factors is recognized in other comprehensive income. For the three months ended March 31, 2013 and 2012, there were no changes in the portion of impairments recognized in earnings for those securities that have been impaired due to both credit factors and non-credit factors.

The Company has evaluated its fixed maturity securities in an unrealized loss position and believes the unrealized losses are due primarily to temporary market and sector-related factors rather than to issuer-specific factors. None of these securities are

13

delinquent or in default under financial covenants. Based on its assessment of these issuers, the Company expects them to continue to meet their contractual payment obligations as they become due and does not consider any of these securities to be OTTI.

Preferred Stocks – At March 31, 2013, there were two preferred stocks in an unrealized loss position, with an aggregate fair value of $25 million and a gross unrealized loss of $2 million. One of those preferred stocks with a gross unrealized loss of $0.2 million was rated non-investment grade. Based upon management’s view of the underlying value of these securities, the Company does not consider either of these preferred stocks to be OTTI.

Common Stocks – At March 31, 2013, the Company owned two common stocks in an unrealized loss position with an aggregate fair value of $31 million and an aggregate unrealized loss of $1 million. The Company does not consider these common stocks to be OTTI.

(16)Fair Value Measurements

The Company’s fixed maturity and equity securities available for sale and its arbitrage trading account securities are carried at fair value. Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for similar assets in active markets. Level 3 inputs are unobservable inputs for the asset or liability. Unobservable inputs may only be used to measure fair value to the extent that observable inputs are not available.

Because many fixed maturity securities do not trade on a daily basis, the Company utilizes pricing models and processes which may include benchmark curves, benchmarking of like securities, sector groupings and matrix pricing. Market inputs used to evaluate securities include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data. Quoted prices are often unavailable for recently issued securities, securities that are infrequently traded or securities that are only traded in private transactions. For publicly traded securities for which quoted prices are unavailable, the Company determines fair value based on independent broker quotations and other observable market data. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information.

14

The following tables present the assets and liabilities measured at fair value, on a recurring basis, as of March 31, 2013 and December 31, 2012 by Level:

(In thousands)	Total		Level 1		Level 2		Level 3
March 31, 2013
Assets:
Fixed maturity securities available for sale:
U.S. government and agency	$	875,712	$	—	$	875,712	$	—
State and municipal	4,409,616		—		4,409,616		—
Mortgage-backed securities	1,544,913		—		1,544,913		—
Corporate	3,571,079		—		3,515,310		55,769
Foreign	1,161,494		—		1,161,494		—
Total fixed maturity securities available for sale	11,562,814		—		11,507,045		55,769
Equity securities:
Common stocks	295,031		293,793		—		1,238
Preferred stocks	104,355		—		103,969		386
Total equity securities	399,386		293,793		103,969		1,624
Arbitrage trading account	701,223		236,670		463,456		1,097
Total	$	12,663,423	$	530,463	$	12,074,470	$	58,490
Liabilities:
Securities sold but not yet purchased	$	79,965	$	70,580	$	9,383	$	2
December 31, 2012
Assets:
Fixed maturity securities available for sale:
U.S. government and agency	$	898,463	$	—	$	898,463	$	—
State and municipal	4,768,519		—		4,768,519		—
Mortgage-backed securities	1,715,697		—		1,715,697		—
Corporate	3,346,719		—		3,287,654		59,065
Foreign	1,111,607		—		1,111,607		—
Total fixed maturity securities available for sale	11,841,005		—		11,781,940		59,065
Equity securities:
Common stocks	282,066		280,658		—		1,408
Preferred stocks	93,956		—		93,335		621
Total equity securities	376,022		280,658		93,335		2,029
Arbitrage trading account	329,077		233,603		94,546		928
Total	$	12,546,104	$	514,261	$	11,969,821	$	62,022
Liabilities:
Securities sold but not yet purchased	$	121,487	$	114,909	$	6,558	$	20

There were no significant transfers between Levels 1 and 2 during the three months ended March 31, 2013 or during the year ended December 31, 2012.

15

The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2013 and for the year ended December 31, 2012:

			Gains (Losses) Included in
(In thousands)	Beginning Balance		Earnings			Other Comprehensive Income				Purchases			(Sales)			Maturities			Transfer in		Ending Balance
Three months ended March 31, 2013:
Assets:
Fixed maturities available for sale:
Corporate	$	59,065	$	(15	)	$	144			$	14,297		$	(14,255	)	$	(3,467	)	$	—	$	55,769
Total	59,065		(15		)	144				14,297			(14,255		)	(3,467		)	—		55,769
Equity securities available for sale:
Common stocks	1,408		—			—				—			(170		)	—			—		1,238
Preferred stocks	621		—			(235		)		—			—			—			—		386
Total	2,029		—			(235		)		—			(170		)	—			—		1,624
Arbitrage trading account	928		169			—			—	—		—	—			—			—		1,097
Total	$	62,022	$	154		$	(91	)		$	14,297		$	(14,425	)	$	(3,467	)	$	—	$	58,490
Liabilities:
Securities sold but not yet purchased	$	20	$	(18	)	$	—			$	—		$	—		$	—		$	—	$	2
For the year ended December 31, 2012:
Assets:
Fixed maturities available for sale:
Corporate	$	67,828	$	(1,497	)	$	9,622			$	283		$	—		$	(17,171	)	$	—	$	59,065
Total	67,828		(1,497		)	9,622				283			—			(17,171		)	—		59,065
Equity securities available for sale:
Common stocks	1,559		—			—				—			(151		)	—			—		1,408
Preferred stocks	12,303		1,126			(1,737		)		—			(11,071		)	—			—		621
Total	13,862		1,126			(1,737		)		—			(11,222		)	—			—		2,029
Arbitrage trading account	851		(3,534		)	3,570				—			(52		)	—			93		928
Total	$	82,541	$	(3,905	)	$	11,455			$	283		$	(11,274	)	$	(17,171	)	$	93	$	62,022
Liabilities:
Securities sold but not yet purchased	$	21	$	(1	)	$	—			$	—		$	—		$	—		$	—	$	20

There were no significant transfers in or out of Level 3 during the three months ended March 31, 2013 or during the year ended December 31, 2012.

16

(17) Reinsurance

The following is a summary of reinsurance financial information:

	For the Three Months Ended
	March 31,
(In thousands)	2013			2012
Written premiums:
Direct	$	1,400,412		$	1,201,019
Assumed	231,209			200,507
Ceded	(254,655		)	(198,000		)
Total net premiums written	$	1,376,966		$	1,203,526
Earned premiums:
Direct	$	1,240,562		$	1,103,956
Assumed	214,016			179,518
Ceded	(222,459		)	(183,823		)
Total net premiums earned	$	1,232,119		$	1,099,651
Ceded losses incurred	$	110,551		$	85,277

The Company reinsures a portion of its exposures principally to reduce its net liability on individual risks and to protect against catastrophic losses. The Company also cedes premiums to state assigned risk plans and captive insurance companies. Estimated amounts due from reinsurers are reported net of reserves for uncollectible reinsurance of $2 million as of March 31, 2013 and December 31, 2012.

(18) Fair Value of Financial Instruments

The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments:

	March 31, 2013				December 31, 2012
(In thousands)	Carrying Value		Fair Value		Carrying Value		Fair Value
Assets:
Fixed maturity securities	$	11,665,117	$	11,688,324	$	11,943,956	$	11,968,376
Equity securities available for sale	399,386		399,386		376,022		376,022
Arbitrage trading account	701,223		701,223		329,077		329,077
Loans receivable	456,533		462,779		401,961		406,443
Cash and cash equivalents	945,492		945,492		905,670		905,670
Trading account receivables from brokers and clearing organizations	28,720		28,720		446,873		446,873
Due from broker	—		—		14,449		14,449
Liabilities:
Trading account securities sold but not yet purchased	79,965		79,965		121,487		121,487
Due to broker	31,300		31,300		—		—
Junior subordinated debentures	243,258		254,800		243,206		252,000
Senior notes and other debt	1,693,279		1,961,361		1,871,535		2,190,173

The estimated fair values of the Company’s fixed maturity securities, equity securities available for sale and arbitrage trading account securities are based on various valuation techniques that rely on fair value measurements as described in Note 16 above. The fair value of loans receivable are estimated by using current institutional purchaser yield requirements for loans with similar credit characteristics, which is considered a Level 2 input. The fair value of the senior notes and other debt and the junior subordinated debentures is based on spreads for similar securities, which is considered a Level 2 input.

17

(19) Restricted Stock Units

Pursuant to its stock incentive plan, the Company may issue restricted stock units (RSUs) to employees of the Company and its subsidiaries. The RSUs generally vest five years from the award date and are subject to other vesting and forfeiture provisions contained in the award agreement. RSUs are expensed pro-ratably over the vesting period. RSU expenses were $5 million and $7 million for the three months ended March 31, 2013 and 2012, respectively. Grants of RSUs are made periodically, generally every other year. A summary of RSUs issued in the three months ended March 31,2013 and 2012 follows:

($ in thousands)	Units	Fair Value
Three months ended March 31:
2013	36,450	$	1,515
2012	35,000	$	1,218

(20) Business Segments

The Company’s financial results are presented for the following reportable business segments:

• Insurance-Domestic - commercial insurance business, including excess and surplus lines and admitted lines, throughout the United States;

• Insurance-International - insurance business primarily in the United Kingdom, Continental Europe, South America, Canada, Scandinavia, and Australia; and

• Reinsurance-Global - reinsurance business on a facultative and treaty basis, primarily in the United States, United Kingdom, Europe, Australia, and the Asia-Pacific Region.

During the first quarter of 2013, the Company changed the aggregation of its business segments. All domestic insurance operating companies, previously included in the Specialty, Regional and Alternative Markets segments, were aggregated into the Insurance-Domestic segment; all reinsurance operating companies were aggregated into the Reinsurance-Global segment; and all international insurance companies were aggregated into the Insurance-International segment. The segment disclosures for prior periods have been revised to be consistent with the new reportable business segment presentation. The segment disclosures for the years ended December 31, 2012, 2011 and 2010, and as of December 31, 2012 and 2011, have also been included herein, revised for the new reportable business segment presentation.

The accounting policies of the segments are the same as those described in the summary of significant accounting policies. Income tax expense and benefits are calculated based upon the Company’s overall effective tax rate.

18

Summary financial information about the Company's business segments is presented in the following tables.

	Revenues
(In thousands)	Earned Premiums		Investment Income		Other		Total		Pre-Tax Income (Loss)			Net Income (Loss)
Three months ended March 31, 2013:
Insurance-Domestic	$	884,378	$	97,797	$	26,736	$	1,008,911	$	141,350		$	99,408
Insurance-International	171,119		12,061		—		183,180		22,382			15,477
Reinsurance-Global	176,622		22,499		—		199,121		37,941			26,394
Corporate and eliminations (1)	—		3,572		92,016		95,588		(61,419		)	(37,644		)
Net investment gains	—		—		19,969		19,969		19,969			12,980
Total	$	1,232,119	$	135,929	$	138,721	$	1,506,769	$	160,223		$	116,615
Three months ended March 31, 2012:
Insurance-Domestic	$	810,069	$	112,086	$	23,877	$	946,032	$	147,735		$	105,880
Insurance-International	143,885		10,331		—		154,216		15,699			11,112
Reinsurance-Global	145,697		28,687		—		174,384		31,638			23,086
Corporate and eliminations (1)	—		6,515		50,067		56,582		(55,260		)	(35,842		)
Net investment gains	—		—		47,491		47,491		47,491			31,082
Total	$	1,099,651	$	157,619	$	121,435	$	1,378,705	$	187,303		$	135,318
Twelve months ended December 31, 2012:
Insurance-Domestic	$	3,417,022	$	424,787	$	103,133	$	3,944,942	$	578,500		$	412,514
Insurance-International	631,841		45,796		—		677,637		51,639			37,499
Reinsurance-Global	624,653		106,932		—		731,585		103,690			76,584
Corporate and eliminations (1)	—		9,248		249,677		258,925		(242,366		)	(152,807		)
Net investment gains	—		—		210,465		210,465		210,465			136,802
Total	$	4,673,516	$	586,763	$	563,275	$	5,823,554	$	701,928		$	510,592
Twelve months ended December 31, 2011:
Insurance-Domestic	$	3,121,281	$	372,053	$	92,847	$	3,586,181	$	467,126		$	344,521
Insurance-International	508,509		36,958		—		545,467		36,912			28,054
Reinsurance-Global	531,077		97,795		—		628,872		85,271			66,174
Corporate and eliminations (1)	—		19,545		250,438		269,983		(201,704		)	(129,185		)
Net investment gains	—		—		125,481		125,481		125,481			81,647
Total	$	4,160,867	$	526,351	$	468,766	$	5,155,984	$	513,086		$	391,211
Twelve months ended December 31, 2010:
Insurance-Domestic	$	2,963,486	$	385,783	$	85,417	$	3,434,686	$	589,138		$	425,337
Insurance-International	378,693		29,011		—		407,704		15,172			13,050
Reinsurance-Global	493,403		106,862		—		600,265		134,996			99,492
Corporate and eliminations (1)	—		8,869		215,964		224,833		(196,977		)	(128,348		)
Net investment gains	—		—		56,581		56,581		56,581			36,874
Total	$	3,835,582	$	530,525	$	357,962	$	4,724,069	$	598,910		$	446,405

19

Identifiable assets by segment are as follows:

(Dollars in thousands)	March 31, 2013		December 31, 2012		December 31, 2011
Insurance-Domestic	$	14,023,370	$	14,661,476	$	13,126,472
Insurance-International	1,690,937		1,605,448		1,341,907
Reinsurance-Global	3,420,508		3,337,937		3,168,528
Corporate and eliminations	985,819		615,118		766,966
Total	$	20,120,634	$	20,155,896	$	18,403,873

___________

(1) Corporate and eliminations represent corporate revenues and expenses that are not allocated to business segments.

Net premiums earned by major line of business are as follows:

	For the Three Months Ended
	March 31,
(In thousands)	2013		2012
Insurance-Domestic
Other liability	$	295,588	$	273,564
Workers’ compensation	229,011		189,544
Short-tail lines (1)	178,749		173,902
Commercial automobile	116,122		110,367
Products liability	64,908		62,692
Total	884,378		810,069
Insurance-International
Other liability	15,218		15,534
Workers’ compensation	22,889		18,618
Short-tail lines (1)	72,123		52,478
Commercial automobile	34,639		30,668
Products liability	26,250		26,587
Total	171,119		143,885
Reinsurance-Global
Casualty	121,327		105,089
Property	55,295		40,608
Total	176,622		145,697
Total	$	1,232,119	$	1,099,651

_____________________

(1) Short-tail lines includes commercial multi-peril (non-liability), inland and ocean marine, accident and health, fidelity and surety, boiler and machinery and other lines.

(21) Subsequent Event

On May 2, 2013, the Company issued $350 million aggregate principal amount of 5.625% Subordinated Debentures due 2053. Net proceeds from this offering will be used for the repayment of $250 million principal amount of the Company's 6.750% Subordinated Debentures due 2045 on May 26, 2013, which were called for redemption on April 26, 2013; the remainder will be used for general corporate purposes.

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SAFE HARBOR STATEMENT

This is a “Safe Harbor” Statement under the Private Securities Litigation Reform Act of 1995. This document may contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Some of the forward-looking statements can be identified by the use of forward-looking words such as “believes,” “expects,” “potential,” “continued,” “may,” “will,” “should,” “seeks,” “approximately,” “predicts,” “intends,” “plans,” “estimates,” “anticipates,” or the negative version of those words or other comparable words. Any forward-looking statements contained herein, including statements related to our outlook for the industry and for our performance for the year 2013 and beyond, are based upon the Company’s historical performance and on current plans, estimates and expectations. The inclusion of this forward-looking information is not and should not be regarded as a representation by us or any other person that the future plans, estimates or expectations contemplated by us will be achieved. They are subject to various risks and uncertainties, including but not limited to: the cyclical nature of the property casualty industry; the impact of significant competition; the long-tail and potentially volatile nature of the insurance and reinsurance business; product demand and pricing; claims development and the process of estimating reserves; investment risks, including those of our portfolio of fixed maturity securities and investments in equity securities, including investments in financial institutions, municipal bonds, mortgage-backed securities, loans receivable, investment funds, real estate, merger arbitrage and private equity investments; effects of emerging claim and coverage issues; the uncertain nature of damage theories and loss amounts; natural and man-made catastrophic losses, including as a result of terrorist activities; general economic and market activities, including inflation, interest rates and volatility in the credit and capital markets; the impact of the conditions in the financial markets and the global economy, and the potential effect of any legislative, regulatory, accounting or other initiatives taken in response to it, on our results and financial condition; continued availability of capital and financing; the success of our new ventures or acquisitions and the availability of other opportunities; the availability of reinsurance; our retention under the Terrorism Risk Act of 2002, as amended; the ability of our reinsurers to pay reinsurance recoverables owed to us; foreign currency and political risks relating to our international operations; other legislative and regulatory developments, including those related to business practices in the insurance industry; credit risk relating to our policyholders, independent agents and brokers; changes in the ratings assigned to us or our insurance company subsidiaries by rating agencies; the availability of dividends from our insurance company subsidiaries; our ability to attract and retain key personnel and qualified employees; potential difficulties with technology and/or data security; the effectiveness of our controls to ensure compliance with guidelines, policies and legal and regulatory standards; and other risks detailed from time to time in the Company’s filings with the Securities and Exchange Commission (“SEC”). These risks and uncertainties could cause our actual results for the year 2013 and beyond to differ materially from those expressed in any forward-looking statement we make. Any projections of growth in our revenues would not necessarily result in commensurate levels of earnings. Our future financial performance is dependent upon factors discussed in our Annual Report on Form 10-K, elsewhere in this Form 10-Q and our other SEC filings. Forward-looking statements speak only as of the date on which they are made. Except to the extent required by applicable laws, the Company does not undertake any obligation to update or revise any forward-looking statement, whether as a result of new information, future developments or otherwise.

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Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations

Overview

W. R. Berkley Corporation is an insurance holding company that is among the largest commercial lines writers in the United States and operates in three business segments: Insurance-Domestic, Insurance-International and Reinsurance-Global. Our decentralized structure provides us with the flexibility to respond quickly and efficiently to local or specific market conditions and to pursue specialty business niches. It also allows us to be closer to our customers in order to better understand their individual needs and risk characteristics. While providing our business units with certain operating autonomy, our structure allows us to capitalize on the benefits of economies of scale through centralized capital, investment, reinsurance and enterprise risk management, and actuarial, financial and corporate legal staff support. The Company’s primary sources of revenues and earnings are its insurance operations and its investments.

An important part of our strategy is to form new operating units to capitalize on various business opportunities, with 24 of our 49 units formed since 2006. These newer units are focused on important parts of the economy in the U.S., including healthcare, energy and agriculture, and on growing international markets, including Scandinavia, Australia, the Asia-Pacific region and South America. As a result, our international operations have become an increasingly important part of our business.

The profitability of the Company’s insurance business is affected primarily by the adequacy of premium rates. The ultimate adequacy of premium rates is not known with certainty at the time an insurance policy is issued because premiums are determined before claims are reported. The ultimate adequacy of premium rates is affected mainly by the severity and frequency of claims, which are influenced by many factors, including natural and other disasters, regulatory measures and court decisions that define and change the extent of coverage and the effects of economic inflation on the amount of compensation for injuries or losses. General insurance prices are also influenced by available insurance capacity, i.e., the level of policyholders’ surplus employed in the industry, and the industry’s willingness to deploy that capital.

Beginning in 2005, the property casualty insurance market became more competitive and insurance rates decreased across most business lines. Increased competition and the impact of the economic downturn also put pressure on policy terms and conditions. While prices have increased since the beginning of 2011, loss costs are also increasing and current market price levels for certain lines of business remain below the prices required for the Company to achieve its long-term return objectives. With its investments in new businesses, the Company believes it is well-positioned to take advantage of new opportunities. Price changes are reflected in the Company’s results over time as premiums are earned.

The Company’s profitability is also affected by its investment income and investment gains. The Company’s invested assets, which are derived from its own capital and cash flow from its insurance business, are invested principally in fixed maturity securities. The return on fixed maturity securities is affected primarily by general interest rates, as well as the credit quality and duration of the securities. Returns available on fixed maturity investments are at historically low levels. The Company's investment income has been negatively impacted by the low fixed maturity investment returns, and will be further impacted if investment returns remain at this level.

The Company also invests in equity securities, merger arbitrage, private equity investments, investment funds, loans receivable and real estate. The Company's investments in investment funds have experienced, and the Company expects to continue to experience, greater fluctuations in investment income.

Critical Accounting Estimates

The following presents a discussion of accounting policies and estimates relating to reserves for losses and loss expenses, assumed premiums and other-than-temporary impairments of investments. Management believes these policies and estimates are the most critical to its operations and require the most difficult, subjective and complex judgments.

Reserves for Losses and Loss Expenses.To recognize liabilities for unpaid losses, either known or unknown, insurers establish reserves, which is a balance sheet account representing estimates of future amounts needed to pay claims and related expenses with respect to insured events which have occurred. Estimates and assumptions relating to reserves for losses and loss expenses are based on complex and subjective judgments, often including the interplay of specific uncertainties with related accounting and actuarial measurements. Such estimates are also susceptible to change as significant periods of time may elapse between the occurrence of an insured loss, the report of the loss to the insurer, the ultimate determination of the cost of the loss and the insurer’s payment of that loss.

In general, when a claim is reported, claims personnel establish a “case reserve” for the estimated amount of the ultimate payment based upon known information about the claim at that time. The estimate represents an informed judgment based on general reserving practices and reflects the experience and knowledge of the claims personnel regarding the nature

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and value of the specific type of claim. Reserves are also established on an aggregate basis to provide for losses incurred but not reported (“IBNR”) to the insurer, potential inadequacy of case reserves and the estimated expenses of settling claims, including legal and other fees and general expenses of administrating the claims adjustment process. Reserves are established based upon the then current legal interpretation of coverage provided.

In examining reserve adequacy, several factors are considered in estimating the ultimate economic value of losses. These factors include, among other things, historical data, legal developments, changes in social attitudes and economic conditions, including the effects of inflation. The actuarial process relies on the basic assumption that past experience, adjusted judgmentally for the effects of current developments and anticipated trends, is an appropriate basis for predicting future outcomes. Reserve amounts are based on management’s informed estimates and judgments using currently available data. As additional experience and other data become available and are reviewed, these estimates and judgments may be revised. This may result in reserve increases or decreases that would be reflected in our results in periods in which such estimates and assumptions are changed.

Reserves do not represent an exact calculation of liability. Rather, reserves represent an estimate of what management expects the ultimate settlement and claim administration will cost. While the methods for establishing reserves are well tested over time, some of the major assumptions about anticipated loss emergence patterns are subject to unanticipated fluctuation. These estimates, which generally involve actuarial projections, are based on management’s assessment of facts and circumstances then known, as well as estimates of trends in claims severity and frequency, judicial theories of liability and other factors, including the actions of third parties which are beyond the Company’s control. These variables are affected by external and internal events, such as inflation and economic volatility, judicial and litigation trends, reinsurance coverage, legislative changes and claim handling and reserving practices, which make it more difficult to accurately predict claim costs. The inherent uncertainties of estimating reserves are greater for certain types of liabilities where long periods of time elapse before a definitive determination of liability is made. Because setting reserves is inherently uncertain, the Company cannot provide assurance that its current reserves will prove adequate in light of subsequent events.

Loss reserves included in the Company’s financial statements represent management’s best estimates based upon an actuarially derived point estimate and other considerations. The Company uses a variety of actuarial techniques and methods to derive an actuarial point estimate for each operating unit. These methods include paid loss development, incurred loss development, paid and incurred Bornhuetter-Ferguson methods and frequency and severity methods. In circumstances where one actuarial method is considered more credible than the others, that method is used to set the point estimate. For example, the paid loss and incurred loss development methods rely on historical paid and incurred loss data. For new lines of business, where there is insufficient history of paid and incurred claims data, or in circumstances where there have been significant changes in claim practices, the paid and incurred loss development methods would be less credible than other actuarial methods. The actuarial point estimate may also be based on a judgmental weighting of estimates produced from each of the methods considered. Industry loss experience is used to supplement the Company’s own data in selecting “tail factors” and in areas where the Company’s own data is limited. The actuarial data is analyzed by line of business, coverage and accident or policy year, as appropriate, for each operating unit.

The establishment of the actuarially derived loss reserve point estimate also includes consideration of qualitative factors that may affect the ultimate losses. These qualitative considerations include, among others, the impact of re-underwriting initiatives, changes in the mix of business, changes in distribution sources and changes in policy terms and conditions. Examples of changes in terms and conditions that can have a significant impact on reserve levels are the use of aggregate policy limits, the expansion of coverage exclusions, whether or not defense costs are within policy limits, and changes in deductibles and attachment points.

The key assumptions used to arrive at the best estimate of loss reserves are the expected loss ratios, rate of loss cost inflation, and reported and paid loss emergence patterns. Expected loss ratios represent management’s expectation of losses at the time the business is written, before any actual claims experience has emerged. This expectation is a significant determinant of the estimate of loss reserves for recently written business where there is little paid or incurred loss data to consider. Expected loss ratios are generally derived from historical loss ratios adjusted for the impact of rate changes, loss cost trends and known changes in the type of risks underwritten. Expected loss ratios are estimated for each key line of business within each operating unit. Expected loss cost inflation is particularly important for the long-tail lines, such as excess casualty, and claims with a high medical component, such as workers’ compensation. Reported and paid loss emergence patterns are used to project current reported or paid loss amounts to their ultimate settlement value. Loss development factors are based on the historical emergence patterns of paid and incurred losses, and are derived from the Company’s own experience and industry data. The paid loss emergence pattern is also significant to excess and assumed workers’ compensation reserves because those reserves are discounted to their estimated present value based upon such estimated payout patterns. Management believes the estimates and assumptions it makes in the reserving process provide the best estimate of the ultimate cost of settling claims and related expenses with respect to insured events which have occurred; however, different assumptions and variables could lead to significantly different reserve estimates.

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Loss frequency and severity are measures of loss activity that are considered in determining the key assumptions described in our discussion of loss and loss expense reserves, including expected loss ratios, rate of loss cost inflation and reported and paid loss emergence patterns. Loss frequency is a measure of the number of claims per unit of insured exposure, and loss severity is a measure of the average size of claims. Factors affecting loss frequency include the effectiveness of loss controls and safety programs and changes in economic activity or weather patterns. Factors affecting loss severity include changes in policy limits, retentions, rate of inflation and judicial interpretations.

Another factor affecting estimates of loss frequency and severity is the loss reporting lag, which is the period of time between the occurrence of a loss and the date the loss is reported to the Company. The length of the loss reporting lag affects our ability to accurately predict loss frequency (loss frequencies are more predictable for lines with short reporting lags) as well as the amount of reserves needed for incurred but not reported losses (less IBNR is required for lines with short reporting lags). As a result, loss reserves for lines with short reporting lags are likely to have less variation from initial loss estimates. For lines with short reporting lags, which include commercial automobile, primary workers’ compensation, other liability (claims-made) and property business, the key assumption is the loss emergence pattern used to project ultimate loss estimates from known losses paid or reported to date. For lines of business with long reporting lags, which include other liability (occurrence), products liability, excess workers’ compensation and liability reinsurance, the key assumption is the expected loss ratio since there is often little paid or incurred loss data to consider. Historically, the Company has experienced less variation from its initial loss estimates for lines of businesses with short reporting lags than for lines of business with long reporting lags.

The key assumptions used in calculating the most recent estimate of the loss reserves are reviewed each quarter and adjusted, to the extent necessary, to reflect historical changes, current trends and other factors observed. If the actual level of loss frequency and severity are higher or lower than expected, the ultimate losses will be different than management’s estimate. The following table reflects the impact of changes (which could be favorable or unfavorable) in frequency and severity, relative to our assumptions, on our loss estimate for claims occurring in 2012 (dollars in thousands):

	Frequency (+/-)
Severity (+/-)	1%		5%		10%
1%	$	60,260	$	181,379	$	332,777
5%	181,379		307,294		464,689
10%	332,777		464,689		629,579

Our net reserves for losses and loss expenses of approximately $8.5 billion as of March 31, 2013 relate to multiple accident years. Therefore, the impact of changes in frequency or severity for more than one accident year could be significantly higher or lower than the amounts reflected above.

Approximately $1.6 billion, or 19%, of the Company’s net loss reserves as of March 31, 2013 relate to the Reinsurance-Global segment. There is a higher degree of uncertainty and greater variability regarding estimates of assumed loss reserves because those estimates are based, in part, upon information received from ceding companies. If information received from ceding companies is not timely or correct, the Company’s estimate of ultimate losses may not be accurate. Furthermore, due to delayed reporting of claim information by ceding companies, the claim settlement tail for assumed reinsurance is extended. Management considers the impact of delayed reporting in its selection of assumed loss development factors.

Information received from ceding companies is used to set initial expected loss ratios, to establish case reserves and to estimate reserves for incurred but not reported losses on assumed reinsurance business. This information, which is generally provided through reinsurance intermediaries, is gathered through the underwriting process and from periodic claim reports and other correspondence with ceding companies. The Company performs underwriting and claim audits of selected ceding companies to determine the accuracy and completeness of information provided to the Company. The information received from the ceding companies is supplemented by the Company’s own loss development experience with similar lines of business as well as industry loss trends and loss development benchmarks.

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Following is a summary of the Company’s reserves for losses and loss expenses by business segment as of March 31, 2013 and December 31, 2012:

(In thousands)	March 31		December 31,
	2013		2012
Insurance-Domestic	$	6,345,559	$	6,297,773
Insurance-International	536,502		540,769
Reinsurance-Global	1,584,633		1,573,309
Net reserves for losses and loss expenses	8,466,694		8,411,851
Ceded reserves for losses and loss expenses	1,343,149		1,339,235
Gross reserves for losses and loss expenses	$	9,809,843	$	9,751,086

Following is a summary of the Company’s net reserves for losses and loss expenses by major line of business as of March 31, 2013 and December 31, 2012:

(In thousands)	Reported Case Reserves		Incurred But Not Reported		Total
March 31, 2013
Other liability	$	931,703	$	1,845,104	$	2,776,807
Workers’ compensation	1,449,415		1,126,527		2,575,942
Short-tail lines	239,397		209,432		448,829
Commercial automobile	277,563		197,905		475,468
Products liability	280,900		324,115		605,015
Total primary	3,178,978		3,703,083		6,882,061
Reinsurance	647,161		937,472		1,584,633
Total	$	3,826,139	$	4,640,555	$	8,466,694
December 31, 2012
Other liability	$	922,568	$	1,863,465	$	2,786,033
Workers’ compensation	1,427,599		1,114,340		2,541,939
Short-tail lines	240,411		205,272		445,683
Commercial automobile	275,322		204,900		480,222
Products liability	271,854		312,811		584,665
Total primary	3,137,754		3,700,788		6,838,542
Reinsurance	626,962		946,347		1,573,309
Total	$	3,764,716	$	4,647,135	$	8,411,851

Reserves for excess and assumed workers’ compensation business are net of an aggregate net discount of $858 million and $867 million as of March 31, 2013 and December 31, 2012, respectively.

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The following table presents development in our estimate of claims occurring in prior years:

	For the Three Months Ended
	March 31
(In thousands)	2013		2012
Favorable reserve development:
Insurance-Domestic	$	4,180	$	14,070
Insurance-International	3,307		2,562
Reinsurance-Global	16,059		8,542
Total favorable reserve development	$	23,546	$	25,174

For the three months ended March 31, 2013, estimates for claims occurring in prior years decreased by $24 million. The favorable reserve development in 2013 was primarily attributable to accident years 2010 and 2012, and was partially offset by unfavorable reserve development for accident year 2011. The changes in prior year loss reserve estimates are generally the result of ongoing analysis of recent loss development trends. Original estimates are increased or decreased as additional information becomes known regarding individual claims and aggregate claim trends.

Insurance - Domestic - Favorable reserve development in 2013 related primarily to our excess and surplus lines casualty business and our regional companies, although occurring at a lower rate than in 2012. In 2013, we also continued to see favorable reserve development in our excess medical malpractice and excess professional liability lines of business. This favorable reserve development was partially offset by unfavorable development in our primary professional liability and aviation lines of business.

Insurance - International - Reserve development in 2013 was primarily related to property business in the 2012 accident year.

Reinsurance-Global - The favorable development in 2013 was primarily related to the Company's minority participation in a Lloyd's syndicate. The favorable development was concentrated in underwriting years 2010 through 2012 and resulted from lower than expected reported losses.

The Company discounts its liabilities for excess and assumed workers’ compensation business because of the long period of time over which losses are paid. Discounting is intended to appropriately match losses and loss expenses to income earned on investment securities supporting the liabilities. The expected losses and loss expense payout pattern subject to discounting was derived from the Company’s loss payout experience. For non-proportional business, reserves for losses and loss expenses have been discounted using risk-free discount rates determined by reference to the U.S. Treasury yield curve. For proportional business, reserves for losses and loss expenses have been discounted at the statutory rate of 2.2%. As of March 31, 2013, the aggregate blended discount rates ranged from 2.1% to 6.5%, with a weighted average discount rate of 4.4%. The aggregate net discount, after reflecting the effects of ceded reinsurance, was $858 million and $867 million as of March 31, 2013 and December 31, 2012, respectively.

Assumed Reinsurance Premiums. The Company estimates the amount of assumed reinsurance premiums that it will receive under treaty reinsurance agreements at the inception of the contracts. These premium estimates are revised as the actual amount of assumed premiums is reported to the Company by the ceding companies. As estimates of assumed premiums are made or revised, the related amount of earned premiums, commissions and incurred losses associated with those premiums are recorded. Estimated assumed premiums receivable were approximately $56 million and $73 million at March 31, 2013 and December 31, 2012, respectively. The assumed premium estimates are based upon terms set forth in reinsurance agreements, information received from ceding companies during the underwriting and negotiation of agreements, reports received from ceding companies and discussions and correspondence with reinsurance intermediaries. The Company also considers its own view of market conditions, economic trends and experience with similar lines of business. These premium estimates represent management’s best estimate of the ultimate amount of premiums to be received under its assumed reinsurance agreements.

Other-Than-Temporary Impairments (OTTI) of Investments. The cost of securities is adjusted where appropriate to include a provision for decline in value which is considered to be other-than-temporary. An other-than-temporary decline is considered to occur in investments where there has been a sustained reduction in fair value and where the Company does not expect the fair value to recover prior to the time of sale or maturity. Since equity securities do not have a contractual cash flow or maturity, the Company considers whether the price of an equity security is expected to recover within a reasonable period of time.

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The Company classifies its fixed maturity securities and preferred stocks by credit rating, primarily based on ratings assigned by credit rating agencies. For purposes of classifying securities with different ratings, the Company uses the lower rating if two ratings were assigned and the middle rating if three ratings were assigned, unless the Company’s own analysis indicates that the lower rating is more appropriate. Securities that are not rated by a rating agency are evaluated and classified by the Company on a case-by-case basis.

Fixed Maturity Securities – For securities that we intend to sell or, more likely than not, would be required to sell, a decline in value below amortized cost is considered to be OTTI. The amount of OTTI is equal to the difference between amortized cost and fair value at the balance sheet date. For securities that we do not intend to sell or expect to be required to sell, a decline in value below amortized cost is considered to be an OTTI if we do not expect to recover the entire amortized cost basis of a security (i.e., the present value of cash flows expected to be collected is less than the amortized cost basis of the security).

The portion of the decline in value considered to be a credit loss (i.e., the difference between the present value of cash flows expected to be collected and the amortized cost basis of the security) is recognized in earnings. The portion of the decline in value not considered to be a credit loss (i.e., the difference in the present value of cash flows expected to be collected and the fair value of the security) is recognized in other comprehensive income.

Impairment assessments for structured securities, including mortgage-backed securities and asset-backed securities, collateralized debt obligations and corporate debt, are generally evaluated based on the performance of the underlying collateral under various economic and default scenarios that may involve subjective judgments and estimates by management. Modeling these securities involves various factors, such as projected default rates, the nature and realizable value of the collateral, if any, the ability of the issuer to make scheduled payments, historical performance and other relevant economic and performance factors. If an OTTI determination is made, a discounted cash flow analysis is used to ascertain the amount of the credit impairment.

The following table provides a summary of fixed maturity securities in an unrealized loss position as of March 31, 2013:

(Dollars in thousands)	Number of Securities	Aggregate Fair Value		Unrealized Loss
Unrealized loss less than 20% of amortized cost	181	$	1,261,456	$	26,020
Unrealized loss of 20% or greater of amortized cost:
Twelve months and longer	6	2,257		1,272
Total	187	$	1,263,713	$	27,292

A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2013 is presented in the table below.

(Dollars in thousands)	Number of Securities	Aggregate Fair Value		Gross Unrealized Loss
Unrealized loss greater than $5 million	—	$	—	$	—
Unrealized loss less than $5 million
Mortgage-backed securities	12	54,367		2,925
Corporate	9	28,242		3,172
State and municipal	2	24,654		1,264
Foreign	1	11,513		7
Total	24	$	118,776	$	7,368

The Company has evaluated its fixed maturity securities in an unrealized loss position and believes the unrealized loss is due primarily to temporary market and sector-related factors rather than to issuer-specific factors. None of these securities are delinquent or in default under financial covenants. Based on its assessment of these issuers, the Company expects them to continue to meet their contractual payment obligations as they become due and does not consider any of these securities to be OTTI.

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Preferred Stocks – At March 31, 2013, there were two preferred stocks in an unrealized loss position, with an aggregate fair value of $25 million and a gross unrealized loss of $2 million. One of those preferred stocks with a gross unrealized loss of $0.2 million was rated non-investment grade. Based upon management's view of the underlying value of these securities, the Company does not consider either of these preferred stocks to be OTTI.

Common Stocks – At March 31, 2013, the Company owned two common stocks in an unrealized loss position with an aggregate fair value of $31 million and an aggregate unrealized loss of $1 million. The Company does not consider these common stocks to be OTTI.

Loans Receivable – The Company monitors the performance of its loans receivable, including current market conditions for each loan and the ability to collect principal and interest. For loans where the Company determines it is probable that the contractual terms will not be met, an analysis is performed and a valuation reserve is established, if necessary, with a charge to earnings. Loans receivable are reported net of a valuation reserve of $6 million at both March 31, 2013 and December 31, 2012.

The Company monitors the performance of its loans receivable and assesses the ability of the borrower to pay principal and interest based upon loan structure, underlying property values, cash flow and related financial and operating performance of the property and market conditions. Loans receivable with a potential for default are further assessed using discounted cash flow analysis and comparable cost and sales methodologies, if appropriate.

Fair Value Measurements.The Company’s fixed maturity and equity securities available for sale and its trading account securities are carried at fair value. Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for similar assets in active markets. Level 3 inputs are unobservable inputs for the asset or liability. Unobservable inputs may only be used to measure fair value to the extent that observable inputs are not available. The fair value of the vast majority of the Company’s portfolio is based on observable data (other than quoted prices) and, accordingly, is classified as Level 2.

In classifying particular financial securities in the fair value hierarchy, the Company uses its judgment to determine whether the market for a security is active and whether significant pricing inputs are observable. The Company determines the existence of an active market by assessing whether transactions occur with sufficient frequency and volume to provide reliable pricing information. The Company determines whether inputs are observable based on the use of such information by pricing services and external investment managers, the uninterrupted availability of such inputs, the need to make significant adjustments to such inputs and the volatility of such inputs over time. If the market for a security is determined to be inactive or if significant inputs used to price a security are determined to be unobservable, the security is categorized in Level 3 of the fair value hierarchy.

Because many fixed maturity securities do not trade on a daily basis, the Company utilizes pricing models and processes which may include benchmark curves, benchmarking of like securities, sector groupings and matrix pricing. Market inputs used to evaluate securities include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data. Quoted prices are often unavailable for recently issued securities that are infrequently traded or securities that are only traded in private transactions. For publicly traded securities for which quoted prices are unavailable, the Company determines fair value based on independent broker quotations and other observable market data. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial data, projections and business developments of the issuer and other relevant information.

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The following is a summary of pricing sources for the Company's fixed maturity securities available for sale as of March 31, 2013:

(Dollars in thousands)	Carrying Value		Percent of Total
Pricing source:
Independent pricing services	$	10,564,047	91.3	%
Syndicate manager	91,244		0.8	%
Directly by the Company based on:
Observable data	851,754		7.4	%
Cash flow model	55,769		0.5	%
Total	$	11,562,814	100.0	%

Independent pricing services - The vast majority of the Company’s fixed maturity securities available for sale were priced by independent pricing services (generally one U.S. pricing service plus additional pricing services with respect to a limited number of foreign securities held by the Company). The prices provided by the independent pricing services are generally based on observable market data in active markets (e.g., broker quotes and prices observed for comparable securities). The determination of whether markets are active or inactive is based upon the volume and level of activity for a particular asset class. The Company reviews the prices provided by pricing services for reasonableness based upon current trading levels for similar securities. If the prices appear unusual to the Company, they are re-examined and the value is either confirmed or revised. In addition, the Company periodically performs independent price tests of a sample of securities to ensure proper valuation and to verify our understanding of how securities are priced. As of March 31, 2013, the Company did not make any adjustments to the prices provided by the pricing services. Based upon the Company’s review of the methodologies used by the independent pricing services, these securities were classified as Level 2.

Syndicate manager – The Company has a 15% participation in a Lloyd’s syndicate, and the Company’s share of the securities owned by the syndicate is priced by the syndicate’s manager. The majority of the securities are liquid, short duration fixed maturity securities. The Company reviews the syndicate manager’s pricing methodology and audited financial statements and holds discussions with the syndicate manager as necessary to confirm its understanding and agreement with security prices. Based upon the Company’s review of the methodologies used by the syndicate manager, these securities were classified as Level 2.

Observable data – If independent pricing is not available, the Company prices the securities directly. Prices are based on observable market data where available, including current trading levels for similar securities and non-binding quotations from brokers. The Company generally requests two or more quotes. If more than one quote is received, the Company sets a price within the range of quotes received based on its assessment of the credibility of the quote and its own evaluation of the security. The Company generally does not adjust quotes obtained from brokers. Since these securities were priced based on observable data, they were classified as Level 2.

Cash flow model – If the above methodologies are not available, the Company prices securities using a discounted cash flow model based upon assumptions as to prevailing credit spreads, interest rates and interest rate volatility, time to maturity and subordination levels. Discount rates are adjusted to reflect illiquidity where appropriate. These securities were classified as Level 3.

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Results of Operations for the Three Months Ended March 31, 2013 and 2012

Business Segment Results

Following is a summary of gross and net premiums written, premiums earned, loss ratios (losses and loss expenses incurred expressed as a percentage of premiums earned), expense ratios (underwriting expenses expressed as a percentage of premiums earned) and United States Generally Accepted Accounting Principles (“GAAP”) combined ratios (sum of loss ratio and expense ratio) for each of our business segments for the three months ended March 31,2013 and 2012. The GAAP combined ratio represents a measure of underwriting profitability, excluding investment income. A GAAP combined ratio in excess of 100 indicates an underwriting loss; a number below 100 indicates an underwriting profit. See the further discussion of the change to our business segments in Note 20 to the interim consolidated financial statements.

(Dollars in thousands)	2013			2012
Insurance-Domestic:
Gross premiums written	$	1,179,722		$	1,038,434
Net premiums written	986,180			882,943
Net premiums earned	884,378			810,069
Loss ratio	62.4		%	62.9		%
Expense ratio	33.1		%	33.2		%
GAAP combined ratio	95.5		%	96.1		%
Insurance-International:
Gross premiums written	$	251,575		$	200,504
Net premiums written	205,135			167,994
Net premiums earned	171,119			143,885
Loss ratio	55.8		%	57.3		%
Expense ratio	38.0		%	40.3		%
GAAP combined ratio	93.8		%	97.6		%
Reinsurance-Global:
Gross premiums written	$	200,324		$	162,588
Net premiums written	185,651			152,589
Net premiums earned	176,622			145,697
Loss ratio	55.0		%	60.2		%
Expense ratio	36.3		%	37.6		%
GAAP combined ratio	91.3		%	97.8		%
Consolidated:
Gross premiums written	$	1,631,621		$	1,401,526
Net premiums written	1,376,966			1,203,526
Net premiums earned	1,232,119			1,099,651
Loss ratio	60.4		%	61.8		%
Expense ratio	34.3		%	34.7		%
GAAP combined ratio	94.7		%	96.5		%

Net Income to Common Stockholders. The following table presents the Company's net income to common stockholders and net income per diluted share for the three months ended March 31, 2013 and 2012:

(In thousands, except per share data)	2013		2012
Net income to common stockholders	$	116,615	$	135,318
Weighted average diluted shares	141,223		143,411
Net income per diluted share	$	0.83	$	0.94

The Company reported net income of $117 million in 2013 compared to $135 million in 2012. The decrease in net income was primarily due to decreases in after-tax net investment gains of $18 million and in after-tax net investment income of $15 million, partially offset by an increase in after-tax underwriting income of $17 million. The number of weighted average diluted shares decreased as a result of the Company’s repurchases of its common stock in 2012.

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Premiums. Gross premiums written were $1,632 million in 2013, an increase of 16% from $1,402 million in 2012. The growth was due to a combination of rate increases and increased exposures, including expansion into new geographic and product markets. Approximately 76.4% of policies expiring in 2013 were renewed, compared with a 77.5% renewal retention rate for policies expiring in 2012. The average rate (i.e., average premium adjusted for change in exposures) for policies that renewed in 2013 increased 7.3%. Audit premiums were $31 million in 2013 compared with $22 million in 2012.

From 2005 through 2010, the property casualty insurance market was highly competitive and insurance rates decreased across most business lines. Prices began to increase in 2011, and the rate of increase accelerated in 2012. Cumulatively, our average rates have increased 15% since the end of 2010. However, overall loss costs are also generally increasing, and current market price levels for certain lines of business remain below the prices required for the Company to achieve its long-term return objectives. A summary of gross premiums written in 2013 compared with 2012 by line of business within each business segment follows:

• Insurance-Domestic premiums increased 14% to $1,180 million in 2013 from $1,038 million in 2012. Gross premiums increased $67 million (22%) for workers' compensation, $40 million (12%) for other liability, $18 million (8%) for short-tail lines, $13 million (19%) for professional liability and $3 million (2%) for commercial automobile.

• Insurance-International gross premiums increased 25% to $252 million in 2013 from $201 million in 2012. Gross premiums increased $43 million (43%) for short-tail lines, $4 million (22%) for workers' compensation, $2 million (8%) for professional liability, $1 million (5%) for other liability and $1 million (3%) for commercial automobile.

• Reinsurance-Global gross premiums increased 23% to $200 million in 2013 from $163 million in 2012. Gross premiums increased $18 million (36%) for property business and $19 million (18%) for casualty business.

Net premiums written were $1,377 million in 2013, an increase of 14% from $1,204 million in 2012. Ceded reinsurance premiums as a percentage of gross written premiums were 16% in 2013 and 14% in 2012. The increase in the percentage of business ceded was due to expanded reinsurance protection for certain lines of business and to disproportionately higher growth by companies that purchase more reinsurance protection.

Premiums earned increased 12% to $1,232 million in 2013 from $1,100 million in 2012. Insurance premiums (including the impact of rate changes) are generally earned evenly over the policy term, and accordingly we expect to recognize recent rate increases over the upcoming quarters. Premiums earned in 2013 are related to business written during both 2013 and 2012.

Net Investment Income. Following is a summary of net investment income for the three months ended March 31, 2013 and 2012:

($ in thousands)	Amount						Average Annualized Yield
	2013			2012			2013		2012
Fixed maturity securities, including cash and cash equivalents and loans receivable	$	117,836		$	119,288		3.7	%	3.8	%
Arbitrage trading account	3,783			6,481			3.7		8.5
Investment funds	10,934			27,623			5.7		17.8
Equity securities available for sale	2,247			3,150			2.9		3.5
Real estate	3,141			2,176			2.1		2.5
Gross investment income	137,941			158,718			3.7	%	4.5	%
Investment expenses	(2,012		)	(1,099		)
Total	$	135,929		$	157,619		3.7	%	4.5	%

Net investment income decreased 14% to $136 million in 2013 from $158 million in 2012. The decrease in investment income was primarily due to an decrease in income from energy and real estate funds (investment funds are reported on a one quarter lag). The average annualized yield for fixed maturity securities declined from 3.8% to 3.7% due to lower long-term reinvestment yields available in the market. Average invested assets, at cost (including cash and cash equivalents) were $14.8 billion in 2013 and $14.2 billion in 2012.

Insurance Service Fees. The Company is a servicing carrier of workers' compensation assigned risk plans for 20 states and provides insurance program management services to self-insureds, captives, governmental entities, risk retention groups, and insurance companies. Service fees were $27 million in 2013, up from $24 million in 2012, primarily as a result of an increase in fees from assigned risk plans.

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Net Realized Gains on Investment Sales. The Company buys and sells securities on a regular basis in order to maximize its total return on investments. Decisions to sell securities are based on management’s view of the underlying fundamentals of specific securities as well as management’s expectations regarding interest rates, credit spreads, currency values and general economic conditions. Net realized gains on investment sales were $20 million in 2013 compared with $43 million in 2012.

Change in Valuation Allowance, Net of Other-Than-Temporary Impairments. For loans where the Company determines it is probable that the contractual terms will not be met, an analysis is performed and a valuation reserve is established, if necessary, with a charge to earnings. The cost of securities is adjusted where appropriate to include a provision for a decline in value that is considered to be other-than-temporary. In 2012, the valuation allowance for mortgage loans decreased by $7 million. There were no other-than-temporary impairments in 2013 compared with $3 million in 2012.

Revenues from Wholly-Owned Investees. Revenues from wholly-owned investees were derived from aviation-related businesses that provide services to the general aviation market, including fuel and line service, aircraft sales and maintenance, avionics and engineering services and parts fabrication. Revenues from wholly-owned investees increased to $92 million in 2013 from $50 million in 2012, primarily as a result of the acquisition of an aircraft equipment supplier in January 2013.

Losses and Loss Expenses. Losses and loss expenses increased to $745 million in 2013 from $679 million in 2012. The consolidated loss ratio was 60.4% in 2013, down from 61.8% in 2012. Catastrophe losses, net of reinsurance recoveries and reinstatement premiums, were $5 million in 2013 compared with $4 million in 2012. Favorable prior year reserve development was $24 million in 2013 compared with $25 million in 2012, a difference of 0.4 loss ratio points. The loss ratio excluding catastrophe losses and prior year reserve development decreased 1.8 points to 61.9% in 2013 from 63.7% in 2012. A summary of loss ratios in 2013 compared with 2012 by business segment follows:

• Insurance-Domestic - The loss ratio of 62.4% in 2013 was 0.5 points lower than the loss ratio of 62.9% in 2012. Catastrophe losses were $4 million in 2013, the same as in 2012. Favorable prior year reserve development was $4 million in 2013 compared with $14 million in 2012, a difference of 1.2 loss ratio points. The loss ratio excluding catastrophe losses and prior year reserve development decreased 1.6 points to 62.5% in 2013 from 64.1% in 2012.

• Insurance-International - The loss ratio of 55.8% in 2013 was 1.5 points lower than the loss ratio of 57.3% in 2012. Favorable prior year reserve development was $4 million in 2013 compared with $3 million in 2012. The loss ratio excluding catastrophe losses and prior year reserve development decreased 1.5 points to 57.6% in 2013 from 59.1% in 2012 due to favorable pricing and loss cost trends.

• Reinsurance-Global - The loss ratio of 55.0% in 2013 was 5.2 points lower than the loss ratio of 60.2% in 2012. There were $1 million in catastrophe losses in 2013 compared with none in 2012, an increase of 0.6 loss ratio points. Favorable prior year reserve development was $16 million in 2013 and $8 million in 2012, a difference of 3.3 loss ratio points. The loss ratio excluding catastrophe losses and prior year reserve development decreased 2.5 points to 63.5% in 2013 from 66.0% in 2012 due to lower property losses.

Other Operating Costs and Expenses. Following is a summary of other operating costs and expenses:

(In thousands)	2013		2012
Underwriting expenses	$	422,213	$	382,023
Service expenses	22,305		19,592
Net foreign currency losses (gains)	1,947		(1,434		)
Other costs and expenses	35,139		31,598
Total	$	481,604	$	431,779

Underwriting expenses are comprised of commissions paid to agents and brokers, premium taxes and other assessments and internal underwriting costs. Underwriting expenses increased 11% compared with an increase in net premiums written of 14%. The expense ratio (underwriting expenses expressed as a percentage of premiums earned) was 34.3% in 2013 and 34.7% in 2012, reflecting the increase in earned premium.

Service expenses, which represent the costs associated with the fee-based businesses, increased 14% to $22 million. The increase was due to an increase in general and administrative expenses related to fee-based business.

Net foreign currency losses (gains) result from transactions denominated in a currency other than the operating unit’s functional currency.

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Other costs and expenses were $35 million in 2013 compared with $32 million in 2012. Other costs and expenses represent general and administrative expenses of the parent company and other expenses not allocated to business segments, including the cost of certain long-term incentive plans.

Expenses from Wholly-Owned Investees. Expenses from wholly-owned investees represent costs associated with aviation-related businesses that include cost of goods sold related to aircraft and other sales, labor and equipment costs related to repairs and other services and general and administrative expenses. Expenses from wholly-owned investees increased to $89 million in 2013 from $51 million in 2012 primarily due to an acquisition in January 2013.

Interest Expense. Interest expense was $31 million in 2013 compared with $29 million in 2012. The Company issued $350 million of 4.625% senior notes in March 2012 and repaid $200 million of 5.875% senior notes that matured in February 2013. As described below, in May 2013, the Company issued $350 aggregate principal amount of 5.625% Subordinated Debentures due 2053, the proceeds of which will be used in part to redeem the Company's 6.750% Subordinated Debentures due 2045.

Income Taxes. The effective income tax rate was 27% in 2013 compared to 28% in 2012. The effective income tax rate differs from the federal income tax rate of 35% primarily because of tax-exempt investment income. Tax exempt investment income comprised a slightly higher portion of the 2013 pre-tax income and as such had a more impact on the effective tax rate for 2013 compared with 2012.

The Company has not provided U.S. deferred income taxes on the undistributed earnings of approximately $104 million of its non-U.S. subsidiaries since these earnings are intended to be permanently reinvested in the non-U.S. subsidiaries. However, in the future, if such earnings were distributed to the Company, taxes of approximately $9 million, assuming all tax credits are realized, would be payable on such undistributed earnings and would be reflected in the tax provision for the year in which these earnings are no longer intended to be permanently reinvested in the foreign subsidiary.

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Investments

As part of its investment strategy, the Company establishes a level of cash and highly liquid short-term and intermediate-term securities that, combined with expected cash flow, it believes is adequate to meet its payment obligations.

The Company also attempts to maintain an appropriate relationship between the average duration of the investment portfolio and the approximate duration of its liabilities (i.e., policy claims and debt obligations). The average duration of the fixed maturity portfolio was 3.3 years at March 31, 2013 and 3.4 years at December 31, 2012. The Company’s fixed maturity investment portfolio and investment-related assets as of March 31, 2013 were as follows:

(Dollars in thousands)	Carrying Value		Percent of Total
Fixed maturity securities:
U.S. government and government agencies	$	875,712	6.0	%
State and municipal:
Special revenue	2,018,194		13.8	%
Pre-refunded (1)	853,418		5.8	%
State general obligation	859,481		5.9	%
Local general obligation	374,158		2.6	%
Corporate backed	370,490		2.5	%
Total state and municipal	4,475,741		30.6	%
Mortgage-backed securities:
Agency	1,057,039		7.2	%
Residential-Prime	209,938		1.4	%
Residential-Alt A	99,751		0.7	%
Commercial	209,366		1.4	%
Total mortgage-backed securities	1,576,094		10.8	%
Corporate:
Industrial	1,548,214		10.6	%
Financial	859,566		5.9	%
Asset-backed	822,825		5.6	%
Utilities	219,618		1.5	%
Other	125,853		0.9	%
Total corporate	3,576,076		24.5	%
Foreign government and foreign government agencies	1,161,494		8.0	%
Total fixed maturity securities	11,665,117		79.9	%
Equity securities
Common stocks	295,031		2.0	%
Preferred stocks	104,355		0.7	%
Total equity securities	399,386		2.7	%
Investment funds	793,603		5.4	%
Real estate	588,777		4.0	%
Arbitrage trading account	701,223		4.8	%
Loans receivable	456,533		3.1	%
Total investments	$	14,604,639	100.0	%

______________    

(1) Pre-refunded securities are securities for which an escrow account has been established to fund the remaining payments of principal and interest through maturity. Such escrow accounts are funded almost exclusively with U.S. Treasury and U.S. government agency securities.

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Fixed Maturity Securities. The Company’s investment policy with respect to fixed maturity securities is generally to purchase instruments with the expectation of holding them to their maturity. However, management of the available for sale portfolio is considered necessary to maintain an approximate matching of assets and liabilities as well as to adjust the portfolio as a result of changes in financial market conditions and tax considerations.

The Company’s philosophy related to holding or selling fixed maturity securities is based on its objective of maximizing total return. The key factors that management considers in its investment decisions as to whether to hold or sell fixed maturity securities are its view of the underlying fundamentals of specific securities as well as its expectations regarding interest rates, credit spreads and currency values. In a period in which management expects interest rates to rise, the Company may sell longer duration securities in order to mitigate the impact of an interest rate rise on the fair value of the portfolio. Similarly, in a period in which management expects credit spreads to widen, the Company may sell lower quality securities, and in a period in which management expects certain foreign currencies to decline in value, the Company may sell securities denominated in those foreign currencies. The sale of fixed maturity securities in order to achieve the objective of maximizing total return may result in realized gains; however, there is no reason to expect these gains to continue in future periods.

At March 31, 2013, investments in foreign fixed maturity securities were as follows:

(Dollars in thousands)	Government		Corporate		Total
Australia	$	243,737	$	139,062	$	382,799
Canada	136,247		49,419		185,666
United Kingdom	111,644		58,200		169,844
Argentina	133,466		29,511		162,977
Germany	72,055		—		72,055
Norway	64,936				64,936
Brazil	49,550		—		49,550
Supranational (1)	38,672		—		38,672
Netherlands	—		13,057		13,057
Switzerland	—		11,279		11,279
Singapore	6,840		—		6,840
Uruguay	3,400		—		3,400
New Zealand	419		—		419
Total	$	860,966	$	300,528	$	1,161,494

_______________

(1) Supranational represents investments in the North American Development Bank, European Investment Bank and Inter-American Development Bank.

Equity Securities. Equity securities primarily represent investments in high-dividend yielding common and preferred stocks issued by large market capitalization companies.

Investment Funds. At March 31, 2013, the carrying value of investment funds was $794 million, including investments in real estate funds of $379 million and investments in energy funds of $147 million.

Real Estate. Real estate is directly owned property held for investment. At March 31, 2013, real estate consists of an office building in operation, three office buildings under development and a long-term ground lease.

Arbitrage Trading Account. The arbitrage trading account is comprised of direct investments in arbitrage securities. Merger arbitrage is the business of investing in the securities of publicly held companies that are the targets in announced tender offers and mergers.

Loans Receivable. Loans receivable, which are carried at amortized cost, have an aggregate cost of $457 million and an aggregate fair value of $463 million at March 31, 2013. Amortized cost of these loans is net of a valuation allowance of $6 million as of March 31, 2013. The six largest loans have an aggregate amortized cost of $243 million and an aggregate fair value of $250 million as of such date and are secured by commercial real estate. These loans earn interest at floating LIBOR-based interest rates and have maturities (inclusive of extension options) through August 2025. The loans are secured by commercial real estate located primarily in New York City, California, Hawaii and Chicago.

35

Market Risk. The fair value of the Company’s investments is subject to risks of fluctuations in credit quality and interest rates. The Company uses various models and stress test scenarios to monitor and manage interest rate risk. The Company attempts to manage its interest rate risk by maintaining an appropriate relationship between the average duration of the investment portfolio and the approximate duration of its liabilities (i.e., policy claims and debt obligations). The average duration for the fixed maturity portfolio was 3.3 years at March 31, 2013 and 3.4 years at December 31, 2012. In addition, the fair value of the Company’s international investments is subject to currency risk. The Company attempts to manage its currency risk by matching its foreign currency assets and liabilities where considered appropriate.

Liquidity and Capital Resources

Cash Flow. Cash flow provided from operating activities increased to $115 million in 2013 from $74 million in 2012 due primarily to an increase in cash flow from underwriting activities, partially offset by higher tax payments. The increase in cash flow from underwriting activities primarily reflects a reduction in the paid loss ratio (paid losses as a percent of earned premiums) to 54% in 2013 from 59% in 2012.

The Company's insurance subsidiaries' principal sources of cash are premiums, investment income, service fees and proceeds from sales and maturities of portfolio investments. The principal uses of cash are payments for claims, taxes, operating expenses and dividends. The Company expects its insurance subsidiaries to fund the payment of losses with cash received from premiums, investment income and fees. The Company targets an average duration for its investment portfolio that is within one year of the average duration of its liabilities so that portions of its investment portfolio mature throughout the claim cycle and are available for the payment of claims if necessary. In the event operating cash flow and proceeds from maturities and prepayments of fixed income securities are not sufficient to fund claim payments and other cash requirements, the remainder of the Company's cash and investments is available to pay claims and other obligations as they become due. The Company's investment portfolio is highly liquid, with approximately 81% invested in cash, cash equivalents and marketable fixed maturity securities as of March 31, 2013. If the sale of fixed maturity securities were to become necessary, a realized gain or loss equal to the difference between the cost and sales price of securities sold would be recognized.

Debt. At March 31, 2013, the Company had senior notes, junior subordinated debentures and other debt outstanding with a carrying value of $1,937 million and a face amount of $1,956 million. The maturities of the outstanding debt are $4 million in 2013, $33 million in 2014, $238 million in 2015, $4 million in 2016, $450 million in 2019, $300 million in 2020, $426 million in 2022, $1 million in 2023, $250 million in 2037 and $250 million in 2045.

In March 2012, the Company issued $350 million of 4.625% senior notes due 2022. In February 2013, the Company repaid $200 million of 5.875% senior notes at maturity. In May 2013, the Company issued $350 million aggregate principal amount of 5.625% Subordinated Debentures due 2053. Net proceeds from this offering will be used to pay $250 million principal amount of the Company's 6.750% Subordinated Debentures on May 26, 2013, which were called for redemption on April 26, 2013; the remainder will be used for general corporate purposes.

Equity. At March 31, 2013, total common stockholders’ equity was $4.4 billion, common shares outstanding were 136,028,287 and stockholders’ equity per outstanding share was $32.19.

Total Capital.Total capitalization (equity, debt and junior subordinated debentures) was $6.3 billion at March 31, 2013. The percentage of the Company’s capital attributable to debt and junior subordinated debentures was 31% at March 31, 2013 and 33% at December 31, 2012.

Item 3. Quantitative and Qualitative Disclosure About Market Risk

Reference is made to the information under “Investments - Market Risk” under the caption “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in this Form 10-Q.

Item 4. Controls and Procedures

Disclosure Controls and Procedures. The Company’s management, including its Chief Executive Officer and Chief Financial Officer, has conducted an evaluation of the effectiveness of the Company’s disclosure controls and procedures pursuant to Securities Exchange Act Rule 13a-14 as of the end of the period covered by this quarterly report. Based on that evaluation, the Chief Executive Officer and Chief Financial Officer concluded that the Company has in place effective controls and procedures designed to ensure that information required to be disclosed by the Company in the reports it files or submits under the Securities Exchange Act of 1934 and the rules thereunder, is recorded, processed, summarized and reported within the time periods specified in the Securities and Exchange Commission’s rules and forms.

36

Changes in Internal Control over Financial Reporting. During the quarter ended March 31, 2013, there were no changes in the Company’s internal control over financial reporting that have materially affected, or are reasonably likely to materially affect, the Company’s internal control over financial reporting.

PART II — OTHER INFORMATION

Item 1.Legal Proceedings

The Company’s subsidiaries are subject to disputes, including litigation and arbitration, arising in the ordinary course of their insurance and reinsurance businesses. The Company’s estimates of the costs of settling such matters are reflected in its aggregate reserves for losses and loss expenses, and the Company does not believe that the ultimate outcome of such matters will have a material adverse effect on its financial condition or results of operations.

Item 1A.Risk Factors

There have been no material changes from the risk factors previously disclosed in the Company’s annual report on Form 10-K for the fiscal year ended December 31, 2012.

Item 2.Unregistered Sales of Equity Securities and Use of Proceeds

No shares were repurchased by the Company during the three months ended March 31, 2013. The maximum number of shares that may be repurchased under the Company's outstanding repurchase plan is 9,068,093.

Item 6.Exhibits

Number
(31.1)	Certification of the Chief Executive Officer pursuant to Rule 13a-14(a)/ 15d-14(a).
(31.2)	Certification of the Chief Financial Officer pursuant to Rule 13a-14(a)/ 15d-14(a).
(32.1)	Certification of the Chief Executive Officer and Chief Financial Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002.

37

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this Report to be signed on its behalf by the undersigned thereunto duly authorized.

		W. R. BERKLEY CORPORATION
Date:	May 6, 2013	/s/ William R. Berkley
		William R. Berkley
		Chairman of the Board and Chief Executive Officer
Date:	May 6, 2013	/s/ Eugene G. Ballard
		Eugene G. Ballard
		Senior Vice President - Chief Financial Officer

38

EX-31.1

Exhibit 31.1

CERTIFICATIONS

I, William R. Berkley, Chairman of the Board and Chief Executive Officer of W. R. Berkley Corporation (the “registrant”), certify that:

1. I have reviewed this quarterly report on Form 10-Q of the registrant;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a) designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b) designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c) evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d) disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a) all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b) any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 6, 2013

/s/ William R. Berkley  

William R. Berkley 

Chairman of the Board and

Chief Executive Officer 

EX-31.2

Exhibit 31.2

CERTIFICATIONS

I, Eugene G. Ballard, Senior Vice President-Chief Financial Officer of W. R. Berkley Corporation (the “registrant”), certify that:

1. I have reviewed this quarterly report on Form 10-Q of the registrant;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a) designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

b) designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

c) evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

d) disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a) all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize and report financial information; and

b) any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: May 6, 2013

/s/ Eugene G. Ballard

Eugene G. Ballard

Senior Vice President -

Chief Financial Officer

EX-32.1

Exhibit 32.1

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report of W. R. Berkley Corporation (the “Company”) on Form 10-Q for the period ended March 31, 2013 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), we, William R. Berkley, Chairman of the Board and Chief Executive Officer of the Company, and Eugene G. Ballard, Senior Vice President-Chief Financial Officer of the Company, certify, pursuant to 18 U.S.C. §1350, as adopted pursuant to §906 of the Sarbanes-Oxley Act of 2002, that:

(1) The Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ William R. Berkley

William R. Berkley

Chairman of the Board and Chief Executive Officer

/s/ Eugene G. Ballard

Eugene G. Ballard

Senior Vice President — Chief Financial Officer

May 6, 2013

A signed original of this written statement required by Section 906 has been provided to W. R. Berkley Corporation (the “Company”) and will be retained by the Company and furnished to the Securities and Exchange Commission or its staff upon request.

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Realized And Unrealized Investment Gains (Losses) (Tables)

3 Months Ended

Mar. 31, 2013

Realized and Unrealized Investment Gains (Losses) [Abstract]

Realized and Unrealized Investment Gains (Losses)

Change In Unrealized Gains (Losses) Of Available For Sales Securities

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Investments in Fixed Maturity Securities (The Amortized Cost and Fair Value of Fixed Maturity Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investments in Fixed Maturity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 798,683
Amortized Cost, Due after one year through five years	3,482,465
Amortized Cost, Due after five years through ten years	2,536,987
Amortized Cost, Due after ten years	2,607,141
Amortized Cost, Mortgage-backed securities	1,528,316
Total investment in fixed maturity securities, Amortized Cost	10,953,592	11,217,954
Fair Value, Due in one year or less	826,292
Fair Value, Due after one year through five years	3,673,747
Fair Value, Due after five years through ten years	2,806,448
Fair Value, Due after ten years	2,800,766
Fair Value, Mortgage-backed securities	1,581,071
Total investments in fixed maturity securities, Fair Value	$ 11,688,324	$ 11,968,376

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Recent Accounting Pronouncements Recent Accounting Pronouncements (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deferred policy acquisition costs	$ 425,070		$ 404,047
Stockholders equity	4,378,541		4,306,217
Other operating expenses	481,604	431,779
Income before income taxes	160,223	187,303	701,928	513,086	598,910
Federal and foreign income taxes	(43,625)	(52,071)
Net Income (Loss)	$ 116,615	$ 135,318	$ 510,592	$ 391,211	$ 446,405
Earnings Per Share, Basic	$ 0.86	$ 0.98
Earnings Per Share, Diluted	$ 0.83	$ 0.94

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Reinsurance (Reinsurance Financial Information) (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reinsurance Disclosures [Abstract]
Written premiums, direct	$ 1,400,412,000	$ 1,201,019,000
Written premiums, assumed	231,209,000	200,507,000
Written premiums, ceded	(254,655,000)	(198,000,000)
Total net premiums written	1,376,966,000	1,203,526,000
Earned premiums, direct	1,240,562,000	1,103,956,000
Earned premiums, assumed	214,016,000	179,518,000
Earned premiums, ceded	(222,459,000)	(183,823,000)
Net premiums earned	1,232,119,000	1,099,651,000	4,673,516,000	4,160,867,000	3,835,582,000
Ceded losses incurred	110,551,000	85,277,000
Uncollectible reinsurance	$ 2,000,000

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Investments in Equity Securities Available for Sale (Investments in Equity Securities Available for Sale) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Cost	$ 306,978	$ 308,175
Gross Unrealized, Gains	95,335	70,205
Gross Unrealized, Losses	(2,927)	(2,358)
Fair Value	399,386	376,022
Carrying Value	399,386	376,022
Common Stock [Member]
Cost	224,378	222,671
Gross Unrealized, Gains	71,995	60,102
Gross Unrealized, Losses	(1,342)	(707)
Fair Value	295,031	282,066
Carrying Value	295,031	282,066
Preferred Stock [Member]
Cost	82,600	85,504
Gross Unrealized, Gains	23,340	10,103
Gross Unrealized, Losses	(1,585)	(1,651)
Fair Value	104,355	93,956
Carrying Value	$ 104,355	$ 93,956

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General (Details)	3 Months Ended
	Mar. 31, 2013
General Policies Disclosure [Abstract]
Federal income tax rate	35.00%

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Investments In Fixed Maturity Securities (Tables)

3 Months Ended

Mar. 31, 2013

Investments in Fixed Maturity Securities [Abstract]

Investments In Fixed Maturity Securities

At March 31, 2013 and December 31, 2012, investments in fixed maturity securities were as follows:

(In thousands)	Amortized Cost		Gross Unrealized					Fair Value		Carrying Value
			Gains		Losses
March 31, 2013
Held to maturity:
State and municipal	$	66,125	$	17,675	$	—		$	83,800	$	66,125
Residential mortgage-backed	31,181		4,977		—			36,158		31,181
Corporate	4,997		555		—			5,552		4,997
Total held to maturity	102,303		23,207		—			125,510		102,303
Available for sale:
U.S. government and government agency	807,341		68,429		(58		)	875,712		875,712
State and municipal	4,110,714		308,121		(9,219		)	4,409,616		4,409,616
Mortgage-backed securities:
Residential (1)	1,293,875		48,550		(6,878		)	1,335,547		1,335,547
Commercial	203,260		6,504		(398		)	209,366		209,366
Corporate	3,370,627		210,832		(10,380		)	3,571,079		3,571,079
Foreign	1,065,472		96,381		(359		)	1,161,494		1,161,494
Total available for sale	10,851,289		738,817		(27,292		)	11,562,814		11,562,814
Total investments in fixed maturity securities	$	10,953,592	$	762,024	$	(27,292	)	$	11,688,324	$	11,665,117
December 31, 2012
Held to maturity:
State and municipal	$	65,190	$	18,529	$	—		$	83,719	$	65,190
Residential mortgage-backed	32,764		5,286		—			38,050		32,764
Corporate	4,997		605		—			5,602		4,997
Total held to maturity	102,951		24,420		—			127,371		102,951
Available for sale:
U.S. government and government agency	827,591		72,532		(1,660		)	898,463		898,463
State and municipal	4,449,238		328,974		(9,693		)	4,768,519		4,768,519
Mortgage-backed securities:
Residential (1)	1,395,739		53,846		(7,456		)	1,442,129		1,442,129
Commercial	268,671		5,641		(744		)	273,568		273,568
Corporate	3,144,480		214,322		(12,083		)	3,346,719		3,346,719
Foreign	1,029,284		83,347		(1,024		)	1,111,607		1,111,607
Total available for sale	11,115,003		758,662		(32,660		)	11,841,005		11,841,005
Total investments in fixed maturity securities	$	11,217,954	$	783,082	$	(32,660	)	$	11,968,376	$	11,943,956

___________

(1) Gross unrealized losses for residential mortgage-backed securities include $1,925,000 and $3,037,000 as of March 31, 2013 and December 31, 2012, respectively, related to the non-credit portion of other-than-temporary impairments (“OTTI”) recognized in other comprehensive income.

The Amortized Cost And Fair Value of Fixed Maturity Securities

The amortized cost and fair value of fixed maturity securities at March 31, 2013, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations.

(In thousands)	Amortized Cost		Fair Value
Due in one year or less	$	798,683	$	826,292
Due after one year through five years	3,482,465		3,673,747
Due after five years through ten years	2,536,987		2,806,448
Due after ten years	2,607,141		2,800,766
Mortgage-backed securities	1,528,316		1,581,071
Total	$	10,953,592	$	11,688,324

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Industry Segments (Financial Information of Company Operating Segments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Earned Premiums	$ 1,232,119		$ 1,099,651		$ 4,673,516		$ 4,160,867		$ 3,835,582
Investment Income and Funds	135,929		157,619		586,763		526,351		530,525
Other Revenues	138,721		121,435		563,275		468,766		357,962
Total revenues	1,506,769		1,378,705		5,823,554		5,155,984		4,724,069
Pre-Tax Income (Loss)	160,223		187,303		701,928		513,086		598,910
Net Income (Loss)	116,615		135,318		510,592		391,211		446,405
Insurance-Domestic Segment [Member] [Domain]
Earned Premiums	884,378		810,069		3,417,022		3,121,281		2,963,486
Investment Income and Funds	97,797		112,086		424,787		372,053		385,783
Other Revenues	26,736		23,877		103,133		92,847		85,417
Total revenues	1,008,911		946,032		3,944,942		3,586,181		3,434,686
Pre-Tax Income (Loss)	141,350		147,735		578,500		467,126		589,138
Net Income (Loss)	99,408		105,880		412,514		344,521		425,337
Insurance-International Segment [Member] [Domain]
Earned Premiums	171,119		143,885		631,841		508,509		378,693
Investment Income and Funds	12,061		10,331		45,796		36,958		29,011
Other Revenues	0		0		0		0		0
Total revenues	183,180		154,216		677,637		545,467		407,704
Pre-Tax Income (Loss)	22,382		15,699		51,639		36,912		15,172
Net Income (Loss)	15,477		11,112		37,499		28,054		13,050
Reinsurance-Global Segment [Member] [Domain]
Earned Premiums	176,622		145,697		624,653		531,077		493,403
Investment Income and Funds	22,499		28,687		106,932		97,795		106,862
Other Revenues	0		0		0		0		0
Total revenues	199,121		174,384		731,585		628,872		600,265
Pre-Tax Income (Loss)	37,941		31,638		103,690		85,271		134,996
Net Income (Loss)	26,394		23,086		76,584		66,174		99,492
Corporate, Other and Eliminations Segment [Member]
Earned Premiums	0	[1]	0	[1]	0	[1]	0	[1]	0	[1]
Investment Income and Funds	3,572	[1]	6,515	[1]	9,248	[1]	19,545	[1]	8,869	[1]
Other Revenues	92,016	[1]	50,067	[1]	249,677	[1]	250,438	[1]	215,964	[1]
Total revenues	95,588	[1]	56,582	[1]	258,925	[1]	269,983	[1]	224,833	[1]
Pre-Tax Income (Loss)	(61,419)	[1]	(55,260)	[1]	(242,366)	[1]	(201,704)	[1]	(196,977)	[1]
Net Income (Loss)	(37,644)	[1]	(35,842)	[1]	(152,807)	[1]	(129,185)	[1]	(128,348)	[1]
Net Investment Gains Segment [Member]
Earned Premiums	0		0		0		0		0
Investment Income and Funds	0		0		0		0		0
Other Revenues	19,969		47,491		210,465		125,481		56,581
Total revenues	19,969		47,491		210,465		125,481		56,581
Pre-Tax Income (Loss)	19,969		47,491		210,465		125,481		56,581
Net Income (Loss)	$ 12,980		$ 31,082		$ 136,802		$ 81,647		$ 36,874

[1] Corporate and eliminations represent corporate revenues and expenses that are not allocated to business segments.

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Net Investment Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income (Losses) from Investment Funds	$ 137,941	$ 158,718
Investment expense	(2,012)	(1,099)
Net investment income	135,929	157,619	586,763	526,351	530,525
Fixed Maturity Securities, Including Cash [Member]
Income (Losses) from Investment Funds	117,836	119,288
Investment Funds [Member]
Income (Losses) from Investment Funds	10,934	27,623
Arbitrage Trading Account and Funds [Member]
Income (Losses) from Investment Funds	3,783	6,481
Equity Securities Available For Sale [Member]
Income (Losses) from Investment Funds	2,247	3,150
Real Estate [Member]
Income (Losses) from Investment Funds	$ 3,141	$ 2,176

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Subsequent event Subsequent event (Details) (Subsequent Event [Member], USD $)	May 02, 2013 Subordinated Debentures Due 2053 [Member]	May 26, 2013 Subordinated Debentures Due 2045 [Member]
Subsequent Event [Line Items]
Debt Instrument, Face Amount	$ 350,000,000	$ 250,000,000
Debt Instrument, Interest Rate, Stated Percentage	5.625%	6.75%

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Fair Value of Financial Instruments (Carrying Amounts and Estimated Fair Values of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Assets
Fixed maturity securities	$ 11,665,117	$ 11,943,956
Fixed maturity securities, fair value	11,688,324	11,968,376
Equity securities available for sale	399,386	376,022
Equity securities available for sale, fair value	399,386	376,022
Arbitrage trading account	701,223	329,077
Arbitrage trading account, fair value	701,223	329,077
Loans receivable	456,533	401,961
Loans receivable, fair value	462,779	406,443
Cash and cash equivalents	945,492	905,670	1,082,407	911,742
Cash and cash equivalents, fair value	945,492	905,670
Trading account receivables from brokers and clearing organizations	28,720	446,873
Trading account receivables from brokers and clearing organizations, fair value	28,720	446,873
Due from broker	0	14,449
Due from broker fair value	0	14,449
Liabilities
Trading account securities sold but not yet purchased	79,965	121,487
Trading account securities sold but not yet purchased, fair value	79,965	121,487
Due to broker	31,300	0
Due to broker, fair value	31,300	0
Junior subordinated debentures	243,258	243,206
Junior subordinated debentures, fair value	254,800	252,000
Senior notes and other debt	1,693,279	1,871,535
Senior notes and other debt, fair value	$ 1,961,361	$ 2,190,173

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Fair Value Of Financial Instruments

3 Months Ended

Mar. 31, 2013

Fair Value Of Financial Instruments [Abstract]

Fair Value Of Financial Instruments

Fair Value of Financial Instruments

The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments:

	March 31, 2013				December 31, 2012
(In thousands)	Carrying Value		Fair Value		Carrying Value		Fair Value
Assets:
Fixed maturity securities	$	11,665,117	$	11,688,324	$	11,943,956	$	11,968,376
Equity securities available for sale	399,386		399,386		376,022		376,022
Arbitrage trading account	701,223		701,223		329,077		329,077
Loans receivable	456,533		462,779		401,961		406,443
Cash and cash equivalents	945,492		945,492		905,670		905,670
Trading account receivables from brokers and clearing organizations	28,720		28,720		446,873		446,873
Due from broker	—		—		14,449		14,449
Liabilities:
Trading account securities sold but not yet purchased	79,965		79,965		121,487		121,487
Due to broker	31,300		31,300		—		—
Junior subordinated debentures	243,258		254,800		243,206		252,000
Senior notes and other debt	1,693,279		1,961,361		1,871,535		2,190,173

The estimated fair values of the Company’s fixed maturity securities, equity securities available for sale and arbitrage trading account securities are based on various valuation techniques that rely on fair value measurements as described in Note 16 above. The fair value of loans receivable are estimated by using current institutional purchaser yield requirements for loans with similar credit characteristics, which is considered a Level 2 input. The fair value of the senior notes and other debt and the junior subordinated debentures is based on spreads for similar securities, which is considered a Level 2 input.

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Acquistions intangible (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Business Acquisition [Line Items]
Percentage acquired	51.00%	49.00%
Purchase amount	$ 43,000,000	$ 43,000,000
Amortization of Acquired Intangible Assets	0
Acquired Indefinite-lived Intangible Assets [Line Items]	$ 3,000,000

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Reinsurance (Tables)

3 Months Ended

Mar. 31, 2013

Reinsurance Disclosures [Abstract]

Reinsurance Financial Information

The following is a summary of reinsurance financial information:

	For the Three Months Ended
	March 31,
(In thousands)	2013			2012
Written premiums:
Direct	$	1,400,412		$	1,201,019
Assumed	231,209			200,507
Ceded	(254,655		)	(198,000		)
Total net premiums written	$	1,376,966		$	1,203,526
Earned premiums:
Direct	$	1,240,562		$	1,103,956
Assumed	214,016			179,518
Ceded	(222,459		)	(183,823		)
Total net premiums earned	$	1,232,119		$	1,099,651
Ceded losses incurred	$	110,551		$	85,277

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Industry Segments (Net Premiums Earned By Major Line of Business) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net premiums earned	$ 1,232,119	$ 1,099,651	$ 4,673,516	$ 4,160,867	$ 3,835,582
Insurance-Domestic Segment [Member] [Domain]
Net premiums earned	884,378	810,069	3,417,022	3,121,281	2,963,486
Insurance-International Segment [Member] [Domain]
Net premiums earned	171,119	143,885	631,841	508,509	378,693
Reinsurance-Global Segment [Member] [Domain]
Net premiums earned	176,622	145,697	624,653	531,077	493,403
Property [Member] | Insurance-Domestic Segment [Member] [Domain]
Net premiums earned	178,749	173,902
Property [Member] | Insurance-International Segment [Member] [Domain]
Net premiums earned	72,123	52,478
Property [Member] | Reinsurance-Global Segment [Member] [Domain]
Net premiums earned	55,295	40,608
Commercial Automobile [Member] | Insurance-Domestic Segment [Member] [Domain]
Net premiums earned	116,122	110,367
Commercial Automobile [Member] | Insurance-International Segment [Member] [Domain]
Net premiums earned	34,639	30,668
Products Liability [Member] | Insurance-Domestic Segment [Member] [Domain]
Net premiums earned	64,908	62,692
Products Liability [Member] | Insurance-International Segment [Member] [Domain]
Net premiums earned	26,250	26,587
Workers' Compensation [Member] | Insurance-Domestic Segment [Member] [Domain]
Net premiums earned	229,011	189,544
Workers' Compensation [Member] | Insurance-International Segment [Member] [Domain]
Net premiums earned	22,889	18,618
Casualty [Member] | Reinsurance-Global Segment [Member] [Domain]
Net premiums earned	121,327	105,089
Other Liability [Member] | Insurance-Domestic Segment [Member] [Domain]
Net premiums earned	295,588	273,564
Other Liability [Member] | Insurance-International Segment [Member] [Domain]
Net premiums earned	$ 15,218	$ 15,534

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Real Estate Real Estate (Tables)

3 Months Ended

Mar. 31, 2013

Real Estate [Abstract]

Real Estate Investment Financial Statements, Disclosure [Table Text Block]

Investment in real estate represents directly owned property held for investment, as follows:    

	Carrying value as of
	March 31,		December 31,
(In thousands)	2013		2012
Properties in operation	$	264,755	$	282,899
Properties under development	324,022		323,836
Total	$	588,777	$	606,735

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Statements of Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended						3 Months Ended							3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Unrealized Investment Gains (Losses) [Member]		Mar. 31, 2012 Unrealized Investment Gains (Losses) [Member]	Dec. 31, 2011 Unrealized Investment Gains (Losses) [Member]	Mar. 31, 2013 Currency Translation Adjustments [Member]	Mar. 31, 2012 Currency Translation Adjustments [Member]	Mar. 31, 2013 Net Pension Asset [Member]		Mar. 31, 2012 Net Pension Asset [Member]	Mar. 31, 2013 Accumulated Other Comprehensive Income (Loss) [Member]	Mar. 31, 2012 Accumulated Other Comprehensive Income (Loss) [Member]	Mar. 31, 2013 Noncontrolling Interest [Member]	Mar. 31, 2012 Noncontrolling Interest [Member]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Tax, Portion Attributable to Noncontrolling Interest			$ (20,075)	[1]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, before Tax, Portion Attributable to Noncontrolling Interest							0
Beginning of period	4,335,466		517,658		452,420	430,419	(36,676)	(61,239)	(15,351)		(14,329)	465,631	393,259	29,249	7,526
Other comprehensive income (loss) before reclassifications			20,989				(46,623)					(25,634)
Other Comprehensive Income (Loss), Reclassification, Pension and Other Postretirement Benefit Plans, Net Gain (Loss) Recognized in Net Periodic Benefit Cost, Net of Tax									0
Amounts reclassified from AOCI			(13,179)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax							0
Amounts reclassified from AOCI	1,814	824							1,814		824	(11,365)
Other comprehensive income (loss)	(36,999)	38,431	7,810				(46,623)		1,814			(36,999)		40	23
Unrealized investment gain related to non-controlling interest	7,810	22,024	(40)				0		0
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Benefit Cost, before Tax			12,015						2,792	[2]		(17,283)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent												(31,816)
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax			6,896	[3]
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest							0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Tax, Portion Attributable to Noncontrolling Interest			(4,205)						(978)	[3]		5,918
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Available-for-sale Securities												(5,183)
Other Comprehensive Income (Loss), Tax							0
Change in unrealized foreign exchange gains (losses)	(46,623)	15,583					(46,623)	15,583
End of period	4,410,630		525,428		452,420	430,419	(83,299)	(45,656)	(13,537)		(13,505)	428,592	393,259	32,089	8,539
Other than Temporary Impairment Losses, Investments, Portion in Other Comprehensive Income (Loss), Tax, Portion Attributable to Noncontrolling Interest, Available-for-sale Securities												$ (40)

[1] Net investment gains in the consolidated statements of operations.

[2] Other operating costs and expenses in the consolidated statements of operations.

[3] Income tax expense in the consolidated statements of operations.

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Fair Value Measurements Fair Value Measurements (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Equity, Level 1 to Level 2 Transfers, Amount	$ 0
Number Of Available For Sale Equity Securities Continuous Unrealized Loss Position	24
Fair Value, Level 1 to level 2 Transfers, Amount		0
Fair Value,Transfers out of Level 3	0	0
Fair Value, Transfers Into Level 3	$ 0	$ 0

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Loans Receivable (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Loans Receivable [Line Items]
Loans receivable	$ 456,533,000		$ 401,961,000
Valuation allowance of loans receivable	6,182,000		5,620,000
Impaired loans, with a valuation allowance at cost	3,003,000		1,775,000
Impaired loans, without a valuation allowance at cost	30,000,000		31,023,000
Impaired loans, unpaid principal balance	36,003,000		35,872,000
Decrease in valuation allowance	62,000	(6,896,000)
Loans receivable charged off	463,000	85,000
Loans and Leases Receivable, Impaired, Nonperforming, Nonaccrual of Interest	3,000,000
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	700,000	200,000
Aggregate Amortized Cost Of Six Largest Loans	243,000,000
Aggregate Fair Value Of Six Largest Loans	250,000,000
Aggregate Cost Basis Of Loans Considered Impaired	30,000,000
Specific Valuation Allowance [Member]
Loans Receivable [Line Items]
Valuation allowance of loans receivable	3,500,000		3,000,000
General Valuation Allowance [Member]
Loans Receivable [Line Items]
Valuation allowance of loans receivable	$ 2,682,000		$ 2,620,000

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Per Share Data (Weighted Average Number of Common Shares Used In the Computation of Basic and Diluted Earnings per Share) (Details) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share [Abstract]
Basic	136,025	137,814
Diluted	141,223	143,411

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Per Share Data

3 Months Ended

Mar. 31, 2013

Earnings Per Share [Abstract]

Per Share Data

Per Share Data

The Company presents both basic and diluted net income per share (“EPS”) amounts. Basic EPS is calculated by dividing net income by the weighted average number of common shares outstanding during the period. Diluted EPS is based upon the weighted average number of common and common equivalent shares outstanding during the period and is calculated using the treasury stock method for stock incentive plans. Common equivalent shares are excluded from the computation in periods in which they have an anti-dilutive effect. Stock options for which the exercise price exceeds the average market price over the period have an anti-dilutive effect on EPS and, accordingly, are excluded from the calculation.

The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows:

(In thousands)	For the Three Months Ended
	March 31,
	2013	2012
Basic	136,025	137,814
Diluted	141,223	143,411

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Realized and Unrealized Investment Gains (Losses) (Realized and Unrealized Investment Gains (Losses) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Schedule of Cost-method Investments [Line Items]
Fixed maturity securities, gains	$ 10,996,000	$ 14,955,000
Fixed maturity securities, losses	(5,966,000)	(543,000)
Equity securities available for sale	15,245,000	26,238,000
Realized gains on investment funds	194,000.000	1,310,000.000
Other	(500,000)	1,517,000
Sales of investment funds	19,969,000	43,477,000
Less investment impairments recognized in other comprehensive income	0	6,998,000
OTTI	0.000	(2,984,000.000)
Change in valuation allowance, net of other-than-temporary impairments	0	4,014,000
Net investment gains	19,969,000	47,491,000
Income tax expense	(6,989,000)	(16,409,000)
Total net investment gains	$ 12,980,000	$ 31,082,000

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Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value Of Financial Instruments [Abstract]

Carrying Amounts And Estimated Fair Values Of Financial Instruments

The following table presents the carrying amounts and estimated fair values of the Company’s financial instruments:

	March 31, 2013				December 31, 2012
(In thousands)	Carrying Value		Fair Value		Carrying Value		Fair Value
Assets:
Fixed maturity securities	$	11,665,117	$	11,688,324	$	11,943,956	$	11,968,376
Equity securities available for sale	399,386		399,386		376,022		376,022
Arbitrage trading account	701,223		701,223		329,077		329,077
Loans receivable	456,533		462,779		401,961		406,443
Cash and cash equivalents	945,492		945,492		905,670		905,670
Trading account receivables from brokers and clearing organizations	28,720		28,720		446,873		446,873
Due from broker	—		—		14,449		14,449
Liabilities:
Trading account securities sold but not yet purchased	79,965		79,965		121,487		121,487
Due to broker	31,300		31,300		—		—
Junior subordinated debentures	243,258		254,800		243,206		252,000
Senior notes and other debt	1,693,279		1,961,361		1,871,535		2,190,173

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Per Share Data (Tables)

3 Months Ended

Mar. 31, 2013

Earnings Per Share [Abstract]

Weighted Average Number of Common Shares Used In the Computation of Basic and Diluted Earnings per Share

The weighted average number of common shares used in the computation of basic and diluted earnings per share was as follows:

(In thousands)	For the Three Months Ended
	March 31,
	2013	2012
Basic	136,025	137,814
Diluted	141,223	143,411

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Subsequent event (Notes)

3 Months Ended

Mar. 31, 2013

Subsequent Events [Abstract]

Subsequent Events [Text Block]

(21) Subsequent Event

On May 2, 2013, the Company issued $350 million aggregate principal amount of 5.625% Subordinated Debentures due 2053. Net proceeds from this offering will be used for the repayment of $250 million principal amount of the Company's 6.750% Subordinated Debentures due 2045 on May 26, 2013, which were called for redemption on April 26, 2013; the remainder will be used for general corporate purposes.

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Arbitrage Trading Account and Arbitrage Funds (Fair Value and Carrying Value of the Arbitrage Trading Account and Arbitrage Funds and Related Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Arbitrage Trading Account And Arbitrage Funds [Abstract]
Arbitrage trading account	$ 701,223	$ 329,077

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Restricted Stock Units (Tables)

3 Months Ended

Mar. 31, 2013

Restricted Stock Units [Abstract]

Summary Of Restricted Stock Units Issued

A summary of RSUs issued in the three months ended March 31,2013 and 2012 follows:

($ in thousands)	Units	Fair Value
Three months ended March 31:
2013	36,450	$	1,515
2012	35,000	$	1,218

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Recent Accounting Pronouncements Recent Accounting Pronouncements (Tables)

3 Months Ended

Mar. 31, 2013

Recent Accounting Pronouncements [Abstract]

Schedule of Error Corrections and Prior Period Adjustments [Table Text Block]

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Acquistions (Tables)

3 Months Ended

Mar. 31, 2013

Business Combinations [Abstract]

Schedule of Business Acquisitions, by Acquisition [Table Text Block]

The following table summarizes the estimated fair value of net assets acquired and liabilities assumed at the date of acquisition:

(In thousands)	Acquired in 2013
Cash and cash equivalents	$	3,911
Real estate, furniture and equipment	898
Goodwill	19,664
Intangible assets	44,800
Other assets	60,661
Total assets acquired	129,934
Debt	(27,612		)
Other liabilities assumed	(17,076		)
Net assets acquired	$	85,246

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General

3 Months Ended

Mar. 31, 2013

General Policies Disclosure [Abstract]

General

General

The accompanying unaudited consolidated financial statements of W. R. Berkley Corporation and its subsidiaries (the “Company”) have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information. Accordingly, they do not include all the information and notes required by GAAP for annual financial statements. The unaudited consolidated financial statements reflect all adjustments, consisting only of normal recurring items, which are necessary to present fairly the Company’s financial position and results of operations on a basis consistent with the prior audited consolidated financial statements. Operating results for interim periods are not necessarily indicative of the results that may be expected for the year. All significant intercompany accounts and transactions have been eliminated. The preparation of financial statements requires the use of management estimates. For further information related to a description of areas of judgment and estimates and other information necessary to understand the Company’s financial position and results of operations, refer to the audited consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2012. Reclassifications have been made in the 2012 financial statements as originally reported to conform to the presentation of the 2013 financial statements.

The income tax provision has been computed based on the Company’s estimated annual effective tax rate. The effective tax rate for the quarter differs from the federal income tax rate of 35% principally because of tax-exempt investment income.

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Statements of Comprehensive Income (Tables)

3 Months Ended

Mar. 31, 2013

Comprehensive Income [Abstract]

Schedule of Comprehensive Income (Loss) [Table Text Block]

The following table presents the components of the changes in accumulated other comprehensive income (loss) (AOCI) as of and for the three months ended March 31, 2013:

	Unrealized Investment gains					Currency translation adjustments			Net pension asset					Accumulated other comprehensive income (loss)
(In thousands)
Changes in AOCI
Beginning of period	$	517,658				$	(36,676	)	$	(15,351	)			$	465,631
Other comprehensive income (loss) before reclassifications	20,989					(46,623		)	—					(25,634		)
Amounts reclassified from AOCI	(13,179		)			—			1,814					(11,365		)
Other comprehensive income (loss)	7,810					(46,623		)	1,814					(36,999		)
Unrealized investment gain related to non-controlling interest	(40		)			—			—					(40		)
Ending balance	$	525,428				$	(83,299	)	$	(13,537	)			$	428,592
Amounts reclassified from AOCI
Pre-tax	$	(20,075	)	(1	)	$	—		$	2,792		(3	)	$	(17,283	)
Tax effect	6,896			(2	)	—			(978		)	(2	)	5,918
After-tax amounts reclassified	$	(13,179	)			$	—		$	1,814				$	(11,365	)
Other comprehensive income (loss)
Pre-tax	$	12,015				$	(46,623	)	$	2,792				$	(31,816	)
Tax effect	(4,205		)			—			(978		)			(5,183		)
Other comprehensive income (loss)	$	7,810				$	(46,623	)	$	1,814				$	(36,999	)

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Securities In An Unrealized Loss Position (Tables)

3 Months Ended

Mar. 31, 2013

Securities In An Unrealized Loss Position [Abstract]

Securities In An Unrealized Loss Position

The following table summarizes all securities in an unrealized loss position at March 31, 2013 and December 31, 2012 by the length of time those securities have been continuously in an unrealized loss position:

	Less Than 12 Months				12 Months or Greater				Total
(In thousands)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
March 31, 2013
U.S. government and agency	$	24,203	$	58	$	—	$	—	$	24,203	$	58
State and municipal	133,592		1,830		100,664		7,389		234,256		9,219
Mortgage-backed securities	451,452		4,235		44,419		3,041		495,871		7,276
Corporate	348,050		2,425		66,309		7,955		414,359		10,380
Foreign	91,803		309		3,221		50		95,024		359
Fixed maturity securities	1,049,100		8,857		214,613		18,435		1,263,713		27,292
Common stocks	31,119		1,342		—		—		31,119		1,342
Preferred stocks	386		235		24,324		1,350		24,710		1,585
Equity securities	31,505		1,577		24,324		1,350		55,829		2,927
Total	$	1,080,605	$	10,434	$	238,937	$	19,785	$	1,319,542	$	30,219
December 31, 2012
U.S. government and agency	$	69,551	$	1,660	$	—	$	—	$	69,551	$	1,660
State and municipal	152,694		1,639		135,967		8,054		288,661		9,693
Mortgage-backed securities	484,731		3,629		58,292		4,571		543,023		8,200
Corporate	371,781		2,964		70,537		9,119		442,318		12,083
Foreign	95,623		996		11,210		28		106,833		1,024
Fixed maturity securities	1,174,380		10,888		276,006		21,772		1,450,386		32,660
Common stocks	46,725		707		—		—		46,725		707
Preferred stocks	—		—		39,812		1,651		39,812		1,651
Equity securities	46,725		707		39,812		1,651		86,537		2,358
Total	$	1,221,105	$	11,595	$	315,818	$	23,423	$	1,536,923	$	35,018

Non-Investment Grade Fixed Maturity Securities

Fixed Maturity Securities – A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2013 is presented in the table below.

($ in thousands)	Number of Securities	Aggregate Fair Value			Gross Unrealized Loss
Unrealized loss greater than $5 million:	—	$	—	—	$	—
Unrealized loss less than $5 million:
Mortgage-backed securities	12	54,367			2,925
Corporate	9	28,242			3,172
State and municipal	2	24,654			1,264
Foreign	1	11,513			7
Total	24	$	118,776		$	7,368

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Investments in Fixed Maturity Securities (Investments in Fixed Maturity Securities) (Details) (USD $)	Mar. 31, 2013		Dec. 31, 2012
Total held to maturity, Amortized Cost	$ 102,303,000		$ 102,951,000
Total held to maturity, Gross Unrealized Gains	23,207,000		24,420,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	125,510,000		127,371,000
Total held to maturity, Carrying Value	102,303,000		102,951,000
Total available for sale, Amortized Cost	10,851,289,000		11,115,003,000
Total available for sale, Gross Unrealized Gains	738,817,000		758,662,000
Total available for sale, Gross Unrealized Losses	(27,292,000)		(32,660,000)
Total available for sale, Fair Value	11,562,814,000		11,841,005,000
Total available for sale, Carrying Value	11,562,814,000		11,841,005,000
Total investment in fixed maturity securities, Amortized Cost	10,953,592,000		11,217,954,000
Total investments in fixed maturity securities, Gross Unrealized Gains	762,024,000		783,082,000
Total investments in fixed maturity securities, Gross Unrealized Losses	(27,292,000)		(32,660,000)
Total investments in fixed maturity securities, Fair Value	11,688,324,000		11,968,376,000
Total investments in fixed maturity securities, carrying value	11,665,117,000		11,943,956,000
Minimum ownership of Common stockholders equity	10.00%
U.S. Government And Government Agency [Member]
Total available for sale, Amortized Cost	807,341,000		827,591,000
Total available for sale, Gross Unrealized Gains	68,429,000		72,532,000
Total available for sale, Gross Unrealized Losses	(58,000)		(1,660,000)
Total available for sale, Fair Value	875,712,000		898,463,000
Total available for sale, Carrying Value	875,712,000		898,463,000
State And Municipal [Member]
Total available for sale, Amortized Cost	4,110,714,000		4,449,238,000
Total available for sale, Gross Unrealized Gains	308,121,000		328,974,000
Total available for sale, Gross Unrealized Losses	(9,219,000)		(9,693,000)
Total available for sale, Fair Value	4,409,616,000		4,768,519,000
Total available for sale, Carrying Value	4,409,616,000		4,768,519,000
Residential Mortgage-Backed [Member]
Total available for sale, Amortized Cost	1,293,875,000	[1]	1,395,739,000	[1]
Total available for sale, Gross Unrealized Gains	48,550,000	[1]	53,846,000	[1]
Total available for sale, Gross Unrealized Losses	(6,878,000)	[1]	(7,456,000)	[1]
Total available for sale, Fair Value	1,335,547,000	[1]	1,442,129,000	[1]
Total available for sale, Carrying Value	1,335,547,000	[1]	1,442,129,000	[1]
Non-credit portion of other-than-temporary impairments ("OTTI")	1,925,000		3,037,000
Commercial Mortgage-Backed Securities [Member]
Total available for sale, Amortized Cost	203,260,000		268,671,000
Total available for sale, Gross Unrealized Gains	6,504,000		5,641,000
Total available for sale, Gross Unrealized Losses	(398,000)		(744,000)
Total available for sale, Fair Value	209,366,000		273,568,000
Total available for sale, Carrying Value	209,366,000		273,568,000
Corporate [Member]
Total available for sale, Amortized Cost	3,370,627,000		3,144,480,000
Total available for sale, Gross Unrealized Gains	210,832,000		214,322,000
Total available for sale, Gross Unrealized Losses	(10,380,000)		(12,083,000)
Total available for sale, Fair Value	3,571,079,000		3,346,719,000
Total available for sale, Carrying Value	3,571,079,000		3,346,719,000
Foreign [Member]
Total available for sale, Amortized Cost	1,065,472,000		1,029,284,000
Total available for sale, Gross Unrealized Gains	96,381,000		83,347,000
Total available for sale, Gross Unrealized Losses	(359,000)		(1,024,000)
Total available for sale, Fair Value	1,161,494,000		1,111,607,000
Total available for sale, Carrying Value	1,161,494,000		1,111,607,000
State And Municipal [Member]
Total held to maturity, Amortized Cost	66,125,000		65,190,000
Total held to maturity, Gross Unrealized Gains	17,675,000		18,529,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	83,800,000		83,719,000
Total held to maturity, Carrying Value	66,125,000		65,190,000
Residential Mortgage-Backed [Member]
Total held to maturity, Amortized Cost	31,181,000		32,764,000
Total held to maturity, Gross Unrealized Gains	4,977,000		5,286,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	36,158,000		38,050,000
Total held to maturity, Carrying Value	31,181,000		32,764,000
Corporate [Member]
Total held to maturity, Amortized Cost	4,997,000		4,997,000
Total held to maturity, Gross Unrealized Gains	555,000		605,000
Total held to maturity, Gross Unrealized Losses	0		0
Total held to maturity, Fair Value	5,552,000		5,602,000
Total held to maturity, Carrying Value	$ 4,997,000		$ 4,997,000

[1] Gross unrealized losses for residential mortgage-backed securities include $1,925,000 and $3,037,000 as of March 31, 2013 and December 31, 2012, respectively, related to the non-credit portion of other-than-temporary impairments (“OTTI”) recognized in other comprehensive income.

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Restricted Stock Units (Summary of Restricted Stock Units Issued) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Restricted Stock [Member]
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Restricted Stock Units	36,450	35,000
Restricted Stock Units, Fair Value	$ 1,515	$ 1,218
Additional Paid-In Capital [Member]
Share-Based Compensation Arrangement by Share-based Payment Award [Line Item]
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	$ 4,993	$ 7,447

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Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investments:
Fixed maturity securities	$ 11,665,117	$ 11,943,956
Equity securities available for sale	399,386	376,022
Arbitrage trading account	701,223	329,077
Investment funds	793,603	809,689
Loans receivable	456,533	401,961
Real estate	588,777	606,735
Total investments	14,604,639	14,467,440
Cash and cash equivalents	945,492	905,670
Premiums and fees receivable	1,504,535	1,440,752
Due from reinsurers	1,441,389	1,450,348
Accrued investment income	126,577	127,230
Prepaid reinsurance premiums	345,329	316,309
Deferred policy acquisition costs	425,070	404,047
Real estate, furniture and equipment	271,012	267,227
Goodwill	107,529	87,865
Trading account receivables from brokers and clearing organizations	28,720	446,873
Other assets	320,342	242,135
Total assets	20,120,634	20,155,896
Liabilities:
Reserves for losses and loss expenses	9,809,843	9,751,086
Unearned premiums	2,635,995	2,474,847
Due to reinsurers	298,557	316,388
Trading account securities sold but not yet purchased	79,965	121,487
Deferred federal and foreign income taxes	104,810	82,801
Other liabilities	844,297	959,080
Junior subordinated debentures	243,258	243,206
Senior notes and other debt	1,693,279	1,871,535
Total liabilities	15,710,004	15,820,430
Equity:
Preferred stock, par value $.10 per share: Authorized 5,000,000 shares; issued and outstanding - none	0	0
Common stock, Value issued $.20 per share:Authorized 500,000,000 shares, issued and outstanding, net of treasury shares, 138,274,272 and 137,520,019 shares	47,024	47,024
Additional paid-in capital	949,926	945,166
Retained earnings	4,922,178	4,817,807
Accumulated other comprehensive income	428,592	465,631
Treasury stock, Value, 96,843,646 and 97,597,899 shares	(1,969,179)	(1,969,411)
Total stockholders' equity	4,378,541	4,306,217
Noncontrolling interests	32,089	29,249
Total equity	4,410,630	4,335,466
Total liabilities and equity	$ 20,120,634	$ 20,155,896

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Industry Segments (Tables)

3 Months Ended

Mar. 31, 2013

Industry Segments Disclosure [Abstract]

Financial Information Of Company Operating Segments

	Revenues
(In thousands)	Earned Premiums		Investment Income		Other		Total		Pre-Tax Income (Loss)			Net Income (Loss)
Three months ended March 31, 2013:
Insurance-Domestic	$	884,378	$	97,797	$	26,736	$	1,008,911	$	141,350		$	99,408
Insurance-International	171,119		12,061		—		183,180		22,382			15,477
Reinsurance-Global	176,622		22,499		—		199,121		37,941			26,394
Corporate and eliminations (1)	—		3,572		92,016		95,588		(61,419		)	(37,644		)
Net investment gains	—		—		19,969		19,969		19,969			12,980
Total	$	1,232,119	$	135,929	$	138,721	$	1,506,769	$	160,223		$	116,615
Three months ended March 31, 2012:
Insurance-Domestic	$	810,069	$	112,086	$	23,877	$	946,032	$	147,735		$	105,880
Insurance-International	143,885		10,331		—		154,216		15,699			11,112
Reinsurance-Global	145,697		28,687		—		174,384		31,638			23,086
Corporate and eliminations (1)	—		6,515		50,067		56,582		(55,260		)	(35,842		)
Net investment gains	—		—		47,491		47,491		47,491			31,082
Total	$	1,099,651	$	157,619	$	121,435	$	1,378,705	$	187,303		$	135,318
Twelve months ended December 31, 2012:
Insurance-Domestic	$	3,417,022	$	424,787	$	103,133	$	3,944,942	$	578,500		$	412,514
Insurance-International	631,841		45,796		—		677,637		51,639			37,499
Reinsurance-Global	624,653		106,932		—		731,585		103,690			76,584
Corporate and eliminations (1)	—		9,248		249,677		258,925		(242,366		)	(152,807		)
Net investment gains	—		—		210,465		210,465		210,465			136,802
Total	$	4,673,516	$	586,763	$	563,275	$	5,823,554	$	701,928		$	510,592
Twelve months ended December 31, 2011:
Insurance-Domestic	$	3,121,281	$	372,053	$	92,847	$	3,586,181	$	467,126		$	344,521
Insurance-International	508,509		36,958		—		545,467		36,912			28,054
Reinsurance-Global	531,077		97,795		—		628,872		85,271			66,174
Corporate and eliminations (1)	—		19,545		250,438		269,983		(201,704		)	(129,185		)
Net investment gains	—		—		125,481		125,481		125,481			81,647
Total	$	4,160,867	$	526,351	$	468,766	$	5,155,984	$	513,086		$	391,211
Twelve months ended December 31, 2010:
Insurance-Domestic	$	2,963,486	$	385,783	$	85,417	$	3,434,686	$	589,138		$	425,337
Insurance-International	378,693		29,011		—		407,704		15,172			13,050
Reinsurance-Global	493,403		106,862		—		600,265		134,996			99,492
Corporate and eliminations (1)	—		8,869		215,964		224,833		(196,977		)	(128,348		)
Net investment gains	—		—		56,581		56,581		56,581			36,874
Total	$	3,835,582	$	530,525	$	357,962	$	4,724,069	$	598,910		$	446,405

Identifiable Assets By Segment

Identifiable assets by segment are as follows:

(Dollars in thousands)	March 31, 2013		December 31, 2012		December 31, 2011
Insurance-Domestic	$	14,023,370	$	14,661,476	$	13,126,472
Insurance-International	1,690,937		1,605,448		1,341,907
Reinsurance-Global	3,420,508		3,337,937		3,168,528
Corporate and eliminations	985,819		615,118		766,966
Total	$	20,120,634	$	20,155,896	$	18,403,873

___________

(1) Corporate and eliminations represent corporate revenues and expenses that are not allocated to business segments.

Net Premiums Earned By Major Line Of Business

Net premiums earned by major line of business are as follows:

	For the Three Months Ended
	March 31,
(In thousands)	2013		2012
Insurance-Domestic
Other liability	$	295,588	$	273,564
Workers’ compensation	229,011		189,544
Short-tail lines (1)	178,749		173,902
Commercial automobile	116,122		110,367
Products liability	64,908		62,692
Total	884,378		810,069
Insurance-International
Other liability	15,218		15,534
Workers’ compensation	22,889		18,618
Short-tail lines (1)	72,123		52,478
Commercial automobile	34,639		30,668
Products liability	26,250		26,587
Total	171,119		143,885
Reinsurance-Global
Casualty	121,327		105,089
Property	55,295		40,608
Total	176,622		145,697
Total	$	1,232,119	$	1,099,651

XML

Consolidated Statements of Stockholders' Equity (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Unrealized Investment Gains (Losses) [Member]	Currency Translation Adjustments [Member]	Net Pension Asset [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]
Beginning of period at Dec. 31, 2011		$ 47,024	$ 941,109	$ 4,491,162	$ 430,419	$ (61,239)	$ (14,329)		$ (1,880,790)	$ 7,526
Stock options exercised and restricted units issued, net of tax			(10,139)
Restricted stock units expensed			7,447
Net income to common stockholders	135,232			135,318
Dividends				(11,041)
Unrealized gains (losses) on securities not other-than-temporarily impaired					20,868
Unrealized gains on other-than-temporarily impaired securities					1,133
Net change in period	15,583					15,583
Net change in period	824						824
Stock exercised/vested									20,099
Stock repurchased									(6,532)
Contributions (distributions)										1,076
Net income (loss)	86									(86)
Other comprehensive income (loss), net of tax	38,431									23
End of period at Mar. 31, 2012		47,024	938,417	4,615,439	452,420	(45,656)	(13,505)	393,259	(1,867,223)	8,539
Beginning of period at Dec. 31, 2012	4,335,466	47,024	945,166	4,817,807	517,658	(36,676)	(15,351)	465,631	(1,969,411)	29,249
Stock options exercised and restricted units issued, net of tax			(233)
Restricted stock units expensed			4,993
Net income to common stockholders	116,598			116,615
Dividends				(12,244)
Unrealized gains (losses) on securities not other-than-temporarily impaired					7,047
Unrealized gains on other-than-temporarily impaired securities					723
Net change in period	(46,623)					(46,623)
Net change in period	1,814						1,814	(11,365)
Stock exercised/vested									232
Stock repurchased									0
Contributions (distributions)										2,817
Net income (loss)	17									(17)
Other comprehensive income (loss), net of tax	(36,999)				7,810	(46,623)	1,814	(36,999)		40
End of period at Mar. 31, 2013	$ 4,410,630	$ 47,024	$ 949,926	$ 4,922,178	$ 525,428	$ (83,299)	$ (13,537)	$ 428,592	$ (1,969,179)	$ 32,089

XML

Real Estate Real Estate (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Real Estate [Abstract]
Properties in operation	$ 264,755	$ 282,899
Properties under development	324,022	323,836
Total	$ 588,777	$ 606,735

XML

Net Investment Income (Tables)

3 Months Ended

Mar. 31, 2013

Net Investment Income [Abstract]

Net Investment Income [Table Text Block]

Net investment income consists of the following:

	For the Three Months Ended
	March 31,
(In thousands)	2013			2012
Investment income earned on:
Fixed maturity securities, including cash and cash equivalents and loans receivable	$	117,836		$	119,288
Investment funds	10,934			27,623
Arbitrage trading account	3,783			6,481
Equity securities available for sale	2,247			3,150
Real estate	3,141			2,176
Gross investment income	137,941			158,718
Investment expense	(2,012		)	(1,099		)
Net investment income	$	135,929		$	157,619

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Securities in an Unrealized Loss Position (Non-Investment Grade Fixed Maturity Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Number of securities	24
Aggregate Fair Value	$ 118,776
Gross Unrealized Loss	7,368
Unrealized Loss Less than 5 Million [Member] | Mortgage-Backed Securities [Member]
Number of securities	12
Aggregate Fair Value	54,367
Gross Unrealized Loss	2,925
Unrealized Loss Less than 5 Million [Member] | Corporate [Member]
Number of securities	9
Aggregate Fair Value	28,242
Gross Unrealized Loss	3,172
Unrealized Loss Less than 5 Million [Member] | State And Municipal [Member]
Number of securities	2
Aggregate Fair Value	24,654
Gross Unrealized Loss	1,264
Unrealized Loss Less than 5 Million [Member] | Foreign [Member]
Number of securities	1
Aggregate Fair Value	11,513
Gross Unrealized Loss	7
Unrealized Loss 5 Million or Greater [Member] | Mortgage-Backed Securities [Member]
Number of securities	0
Aggregate Fair Value	0
Gross Unrealized Loss	$ 0

XML

Securities In An Unrealized Loss Position

3 Months Ended

Mar. 31, 2013

Securities In An Unrealized Loss Position [Abstract]

Securities In An Unrealized Loss Position

Securities in an Unrealized Loss Position

The following table summarizes all securities in an unrealized loss position at March 31, 2013 and December 31, 2012 by the length of time those securities have been continuously in an unrealized loss position:

	Less Than 12 Months				12 Months or Greater				Total
(In thousands)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
March 31, 2013
U.S. government and agency	$	24,203	$	58	$	—	$	—	$	24,203	$	58
State and municipal	133,592		1,830		100,664		7,389		234,256		9,219
Mortgage-backed securities	451,452		4,235		44,419		3,041		495,871		7,276
Corporate	348,050		2,425		66,309		7,955		414,359		10,380
Foreign	91,803		309		3,221		50		95,024		359
Fixed maturity securities	1,049,100		8,857		214,613		18,435		1,263,713		27,292
Common stocks	31,119		1,342		—		—		31,119		1,342
Preferred stocks	386		235		24,324		1,350		24,710		1,585
Equity securities	31,505		1,577		24,324		1,350		55,829		2,927
Total	$	1,080,605	$	10,434	$	238,937	$	19,785	$	1,319,542	$	30,219
December 31, 2012
U.S. government and agency	$	69,551	$	1,660	$	—	$	—	$	69,551	$	1,660
State and municipal	152,694		1,639		135,967		8,054		288,661		9,693
Mortgage-backed securities	484,731		3,629		58,292		4,571		543,023		8,200
Corporate	371,781		2,964		70,537		9,119		442,318		12,083
Foreign	95,623		996		11,210		28		106,833		1,024
Fixed maturity securities	1,174,380		10,888		276,006		21,772		1,450,386		32,660
Common stocks	46,725		707		—		—		46,725		707
Preferred stocks	—		—		39,812		1,651		39,812		1,651
Equity securities	46,725		707		39,812		1,651		86,537		2,358
Total	$	1,221,105	$	11,595	$	315,818	$	23,423	$	1,536,923	$	35,018

Fixed Maturity Securities – A summary of the Company’s non-investment grade fixed maturity securities that were in an unrealized loss position at March 31, 2013 is presented in the table below.

($ in thousands)	Number of Securities	Aggregate Fair Value			Gross Unrealized Loss
Unrealized loss greater than $5 million:	—	$	—	—	$	—
Unrealized loss less than $5 million:
Mortgage-backed securities	12	54,367			2,925
Corporate	9	28,242			3,172
State and municipal	2	24,654			1,264
Foreign	1	11,513			7
Total	24	$	118,776		$	7,368

For OTTI of fixed maturity securities that management does not intend to sell or, more likely than not, would not be required to sell, the portion of the decline in value considered to be due to credit factors is recognized in earnings and the portion of the decline in value considered to be due to non-credit factors is recognized in other comprehensive income. For the three months ended March 31, 2013 and 2012, there were no changes in the portion of impairments recognized in earnings for those securities that have been impaired due to both credit factors and non-credit factors.

The Company has evaluated its fixed maturity securities in an unrealized loss position and believes the unrealized losses are due primarily to temporary market and sector-related factors rather than to issuer-specific factors. None of these securities are delinquent or in default under financial covenants. Based on its assessment of these issuers, the Company expects them to continue to meet their contractual payment obligations as they become due and does not consider any of these securities to be OTTI.

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Investment Funds Investment Funds (Tables)

3 Months Ended

Mar. 31, 2013

Investment Funds [Abstract]

Schedule of Investment Funds

Investment funds consist of the following:

	Carrying Value as of				Income (Losses) from Investment Funds
	March 31		December 31,		For the Three Months Ended March 31,
(In thousands)	2013		2012		2013			2012
Real estate	$	379,006	$	373,259	$	(2,001	)	$	8,655
Energy	147,383		146,325		9,466			17,938
Arbitrage	63,462		63,920		(458		)	1,770
Other	203,752		226,185		3,927			(740		)
Total	$	793,603	$	809,689	$	10,934		$	27,623

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Reinsurance

3 Months Ended

Mar. 31, 2013

Reinsurance Disclosures [Abstract]

Reinsurance

Reinsurance

The following is a summary of reinsurance financial information:

	For the Three Months Ended
	March 31,
(In thousands)	2013			2012
Written premiums:
Direct	$	1,400,412		$	1,201,019
Assumed	231,209			200,507
Ceded	(254,655		)	(198,000		)
Total net premiums written	$	1,376,966		$	1,203,526
Earned premiums:
Direct	$	1,240,562		$	1,103,956
Assumed	214,016			179,518
Ceded	(222,459		)	(183,823		)
Total net premiums earned	$	1,232,119		$	1,099,651
Ceded losses incurred	$	110,551		$	85,277

The Company reinsures a portion of its exposures principally to reduce its net liability on individual risks and to protect against catastrophic losses. The Company also cedes premiums to state assigned risk plans and captive insurance companies. Estimated amounts due from reinsurers are reported net of reserves for uncollectible reinsurance of $2 million as of March 31, 2013 and December 31, 2012.

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Fair Value Measurements (Assets and Liabilities Measured At Fair Value, On a Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value Assets Measured On Recurring Basis Total Assets	$ 12,663,423	$ 12,546,104
Fair Value, Assets Measured On Recurring Basis, Arbitrage Trading Account assets	28,720	446,873
Fair Value, Liabilities Measured On Recurring Basis, Securities Sold, Not Yet Purchased	79,965	121,487
Fixed Maturities Securities [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	11,562,814	11,841,005
Fixed Maturities Securities [Member] | U.S. Government And Government Agency [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	875,712	898,463
Fixed Maturities Securities [Member] | State And Municipal [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	4,409,616	4,768,519
Fixed Maturities Securities [Member] | Mortgage-Backed Securities [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	1,544,913	1,715,697
Fixed Maturities Securities [Member] | Corporate [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	3,571,079	3,346,719
Fixed Maturities Securities [Member] | Foreign [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	1,161,494	1,111,607
Equity Securities Available For Sale [Member]
Total Equity Securities Available For Sale	399,386	376,022
Equity Securities Available For Sale [Member] | Common Stock [Member]
Total Equity Securities Available For Sale	295,031	282,066
Equity Securities Available For Sale [Member] | Preferred Stock [Member]
Total Equity Securities Available For Sale	104,355	93,956
Arbitrage Trading Account [Member]
Fair Value, Assets Measured On Recurring Basis, Arbitrage Trading Account assets	701,223	329,077
Level 1 [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	530,463	514,261
Fair Value, Liabilities Measured On Recurring Basis, Securities Sold, Not Yet Purchased	70,580	114,909
Level 1 [Member] | Fixed Maturities Securities [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 1 [Member] | Fixed Maturities Securities [Member] | U.S. Government And Government Agency [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 1 [Member] | Fixed Maturities Securities [Member] | State And Municipal [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 1 [Member] | Fixed Maturities Securities [Member] | Mortgage-Backed Securities [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 1 [Member] | Fixed Maturities Securities [Member] | Corporate [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 1 [Member] | Fixed Maturities Securities [Member] | Foreign [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 1 [Member] | Equity Securities Available For Sale [Member]
Total Equity Securities Available For Sale	293,793	280,658
Level 1 [Member] | Equity Securities Available For Sale [Member] | Common Stock [Member]
Total Equity Securities Available For Sale	293,793	280,658
Level 1 [Member] | Equity Securities Available For Sale [Member] | Preferred Stock [Member]
Total Equity Securities Available For Sale	0	0
Level 1 [Member] | Arbitrage Trading Account [Member]
Fair Value, Assets Measured On Recurring Basis, Arbitrage Trading Account assets	236,670	233,603
Level 2 [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	12,074,470	11,969,821
Fair Value, Liabilities Measured On Recurring Basis, Securities Sold, Not Yet Purchased	9,383	6,558
Level 2 [Member] | Fixed Maturities Securities [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	11,507,045	11,781,940
Level 2 [Member] | Fixed Maturities Securities [Member] | U.S. Government And Government Agency [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	875,712	898,463
Level 2 [Member] | Fixed Maturities Securities [Member] | State And Municipal [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	4,409,616	4,768,519
Level 2 [Member] | Fixed Maturities Securities [Member] | Mortgage-Backed Securities [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	1,544,913	1,715,697
Level 2 [Member] | Fixed Maturities Securities [Member] | Corporate [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	3,515,310	3,287,654
Level 2 [Member] | Fixed Maturities Securities [Member] | Foreign [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	1,161,494	1,111,607
Level 2 [Member] | Equity Securities Available For Sale [Member]
Total Equity Securities Available For Sale	103,969	93,335
Level 2 [Member] | Equity Securities Available For Sale [Member] | Common Stock [Member]
Total Equity Securities Available For Sale	0	0
Level 2 [Member] | Equity Securities Available For Sale [Member] | Preferred Stock [Member]
Total Equity Securities Available For Sale	103,969	93,335
Level 2 [Member] | Arbitrage Trading Account [Member]
Fair Value, Assets Measured On Recurring Basis, Arbitrage Trading Account assets	463,456	94,546
Level 3 [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	58,490	62,022
Fair Value, Liabilities Measured On Recurring Basis, Securities Sold, Not Yet Purchased	2	20
Level 3 [Member] | Fixed Maturities Securities [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	55,769	59,065
Level 3 [Member] | Fixed Maturities Securities [Member] | U.S. Government And Government Agency [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 3 [Member] | Fixed Maturities Securities [Member] | State And Municipal [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 3 [Member] | Fixed Maturities Securities [Member] | Mortgage-Backed Securities [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 3 [Member] | Fixed Maturities Securities [Member] | Corporate [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	55,769	59,065
Level 3 [Member] | Fixed Maturities Securities [Member] | Foreign [Member]
Fair Value Assets Measured On Recurring Basis Total Assets	0	0
Level 3 [Member] | Equity Securities Available For Sale [Member]
Total Equity Securities Available For Sale	1,624	2,029
Level 3 [Member] | Equity Securities Available For Sale [Member] | Common Stock [Member]
Total Equity Securities Available For Sale	1,238	1,408
Level 3 [Member] | Equity Securities Available For Sale [Member] | Preferred Stock [Member]
Total Equity Securities Available For Sale	386	621
Level 3 [Member] | Arbitrage Trading Account [Member]
Fair Value, Assets Measured On Recurring Basis, Arbitrage Trading Account assets	$ 1,097	$ 928

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Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
CASH FROM (USED IN) OPERATING ACTIVITIES:
Net income to common stockholders	$ 116,615	$ 135,318
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains	(19,969)	(47,491)
Depreciation and amortization	20,910	22,212
Noncontrolling interests	(17)	(86)
Investment funds	(10,934)	(27,624)
Stock incentive plans	4,989	7,447
Change in:
Arbitrage trading account	4,485	(2,946)
Premiums and fees receivable	(76,268)	(97,077)
Reinsurance accounts	(34,039)	(16,857)
Deferred policy acquisition costs	(23,608)	(11,483)
Deferred income taxes	22,471	48,160
Reserves for losses and loss expenses	84,569	47,443
Unearned premiums	174,229	115,434
Other liabilities	(148,321)	(98,688)
Net cash from (used in) operating activities	115,112	73,762
CASH FROM (USED IN) INVESTING ACTIVITIES:
Proceeds from sale of fixed matuirty securities	463,388	295,134
Proceeds from sale of equity securities	38,248	32,575
Distributions from (contributions to) investment funds	(22,072)	24,744
Proceeds from maturities and prepayments of fixed maturity securities	667,711	408,647
Purchase of fixed maturity securities	(896,378)	(872,588)
Purchase of equity securities	(35,486)	(68,652)
Real estate purchased	(10,301)	(5,611)
Change in loans receivable	(53,405)	(93,934)
Net additions to real estate, furniture and equipment	(13,042)	(15,055)
Change in balances due to security brokers	43,325	16,146
Payment for business purchased, net of cash acquired	(38,556)	0
Net cash from (used in) investing activities	143,432	(278,594)
CASH FROM (USED IN) FINANCING ACTIVITIES:
Net proceeds from issuance of debt	0	354,315
Net proceeds from stock options exercised	0	3,428
Repayment of debt	(206,280)	(1,684)
Other, net	7,638	10,446
Net cash from (used in) financing activities	(198,642)	366,505
Net impact on cash due to change in foreign exchange rates	(20,080)	8,992
Net change in cash and cash equivalents	39,822	170,665
Cash and cash equivalents at beginning of year	905,670	911,742
Cash and cash equivalents at end of period	$ 945,492	$ 1,082,407

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Consolidated Balance Sheets Balance Sheet (Parentheticals) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Preferred Stock, Par or Stated Value Per Share	$ 100	$ 100
Preferred Stock, Shares Authorized	5,000,000,000	5,000,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common Stock, Par or Stated Value Per Share	$ 200	$ 200
Common Stock, Shares Authorized	500,000,000,000	500,000,000,000
Common Stock, Shares, Issued	136,028,287,000	136,017,732,000
Common Stock, Shares, Outstanding	136,028,287,000	136,017,732,000
Treasury Stock, Shares	99,089,631,000	99,100,186,000

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Net Investment Income

3 Months Ended

Mar. 31, 2013

Net Investment Income [Abstract]

Net Investment Income [Text Block]

Net Investment Income

Net investment income consists of the following:

	For the Three Months Ended
	March 31,
(In thousands)	2013			2012
Investment income earned on:
Fixed maturity securities, including cash and cash equivalents and loans receivable	$	117,836		$	119,288
Investment funds	10,934			27,623
Arbitrage trading account	3,783			6,481
Equity securities available for sale	2,247			3,150
Real estate	3,141			2,176
Gross investment income	137,941			158,718
Investment expense	(2,012		)	(1,099		)
Net investment income	$	135,929		$	157,619

XML

Document and Entity Information	3 Months Ended
	Mar. 31, 2013	Apr. 30, 2013
Entity Information [Line Items]
Entity Registrant Name	BERKLEY W R CORP
Entity Central Index Key	0000011544
Document Type	10-Q
Document Period End Date	Mar. 31, 2013
Amendment Flag	false
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		136,036,887

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Investment Funds Investment Funds (Notes)

3 Months Ended

Mar. 31, 2013

Investment Funds [Abstract]

Investment Funds [Text Block]

Investment Funds

Investment funds consist of the following:

	Carrying Value as of				Income (Losses) from Investment Funds
	March 31		December 31,		For the Three Months Ended March 31,
(In thousands)	2013		2012		2013			2012
Real estate	$	379,006	$	373,259	$	(2,001	)	$	8,655
Energy	147,383		146,325		9,466			17,938
Arbitrage	63,462		63,920		(458		)	1,770
Other	203,752		226,185		3,927			(740		)
Total	$	793,603	$	809,689	$	10,934		$	27,623

The Company's share of the earnings or losses of investment funds is generally reported on a one-quarter lag in order to facilitate the timely completion of the Company's consolidated financial statements.

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Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
REVENUES:
Net premiums written	$ 1,376,966	$ 1,203,526
Change in net unearned premiums	(144,847)	(103,875)
Net premiums earned	1,232,119	1,099,651
Net investment income	135,929	157,619
Insurance service fees	26,736	23,877
Net investment gains:
Net realized gains on investment sales	19,969	43,477
Change in valuation allowance, net of other-than-temporary impairments	0	4,014
Net investment gains	19,969	47,491
Revenues from wholly-owned investees	91,735	49,675
Other income	281	392
Total revenues	1,506,769	1,378,705
OPERATING COSTS AND EXPENSES:
Losses and loss expenses	744,679	679,472
Other operating costs and expenses	481,604	431,779
Expenses from wholly-owned investees	89,152	51,330
Interest expense	31,111	28,821
Total operating costs and expenses	1,346,546	1,191,402
Income before income taxes	160,223	187,303
Income tax expense	(43,625)	(52,071)
Net income before noncontrolling interests	116,598	135,232
Noncontrolling interests	17	86
Net income to common stockholders	$ 116,615	$ 135,318
NET INCOME PER SHARE:
Basic	$ 0.86	$ 0.98
Diluted	$ 0.83	$ 0.94

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Statements Of Cash Flow

3 Months Ended

Mar. 31, 2013

Supplemental Cash Flow Information [Abstract]

Statements Of Cash Flow

Statements of Cash Flow

Interest payments were $53,691,000 and $45,358,000 and income taxes paid were $23,850,000 and $3,249,000 in the three months ended March 31, 2013 and 2012, respectively.

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Acquistions (Notes)

3 Months Ended

Mar. 31, 2013

Business Combinations [Abstract]

Business Combination Disclosure [Text Block]

Acquisitions

In 2012, the Company acquired a 49% interest in a worldwide supplier of after-market original equipment manufacturer (OEM) parts, systems and custom logistic support services for military aircraft operations for $43 million. In January 2013, the Company acquired the remaining 51% of this business for $43 million. The estimated useful lives of the intangible assets acquired range from 2 years to 15 years, with approximately $3 million having an indefinite life.

The following table summarizes the estimated fair value of net assets acquired and liabilities assumed at the date of acquisition:

(In thousands)	Acquired in 2013
Cash and cash equivalents	$	3,911
Real estate, furniture and equipment	898
Goodwill	19,664
Intangible assets	44,800
Other assets	60,661
Total assets acquired	129,934
Debt	(27,612		)
Other liabilities assumed	(17,076		)
Net assets acquired	$	85,246

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Fair Value Measurements

3 Months Ended

Mar. 31, 2013

Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]

Fair Value Measurements

Fair Value Measurements

The Company’s fixed maturity and equity securities available for sale and its arbitrage trading account securities are carried at fair value. Fair value is defined as “the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date.” The Company utilizes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three broad levels. Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for similar assets in active markets. Level 3 inputs are unobservable inputs for the asset or liability. Unobservable inputs may only be used to measure fair value to the extent that observable inputs are not available.

Because many fixed maturity securities do not trade on a daily basis, the Company utilizes pricing models and processes which may include benchmark curves, benchmarking of like securities, sector groupings and matrix pricing. Market inputs used to evaluate securities include benchmark yields, reported trades, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers and reference data. Quoted prices are often unavailable for recently issued securities, securities that are infrequently traded or securities that are only traded in private transactions. For publicly traded securities for which quoted prices are unavailable, the Company determines fair value based on independent broker quotations and other observable market data. For securities traded only in private negotiations, the Company determines fair value based primarily on the cost of such securities, which is adjusted to reflect prices of recent placements of securities of the same issuer, financial projections, credit quality and business developments of the issuer and other relevant information.

The following tables present the assets and liabilities measured at fair value, on a recurring basis, as of March 31, 2013 and December 31, 2012 by Level:

(In thousands)	Total		Level 1		Level 2		Level 3
March 31, 2013
Assets:
Fixed maturity securities available for sale:
U.S. government and agency	$	875,712	$	—	$	875,712	$	—
State and municipal	4,409,616		—		4,409,616		—
Mortgage-backed securities	1,544,913		—		1,544,913		—
Corporate	3,571,079		—		3,515,310		55,769
Foreign	1,161,494		—		1,161,494		—
Total fixed maturity securities available for sale	11,562,814		—		11,507,045		55,769
Equity securities:
Common stocks	295,031		293,793		—		1,238
Preferred stocks	104,355		—		103,969		386
Total equity securities	399,386		293,793		103,969		1,624
Arbitrage trading account	701,223		236,670		463,456		1,097
Total	$	12,663,423	$	530,463	$	12,074,470	$	58,490
Liabilities:
Securities sold but not yet purchased	$	79,965	$	70,580	$	9,383	$	2
December 31, 2012
Assets:
Fixed maturity securities available for sale:
U.S. government and agency	$	898,463	$	—	$	898,463	$	—
State and municipal	4,768,519		—		4,768,519		—
Mortgage-backed securities	1,715,697		—		1,715,697		—
Corporate	3,346,719		—		3,287,654		59,065
Foreign	1,111,607		—		1,111,607		—
Total fixed maturity securities available for sale	11,841,005		—		11,781,940		59,065
Equity securities:
Common stocks	282,066		280,658		—		1,408
Preferred stocks	93,956		—		93,335		621
Total equity securities	376,022		280,658		93,335		2,029
Arbitrage trading account	329,077		233,603		94,546		928
Total	$	12,546,104	$	514,261	$	11,969,821	$	62,022
Liabilities:
Securities sold but not yet purchased	$	121,487	$	114,909	$	6,558	$	20

There were no significant transfers between Levels 1 and 2 during the three months ended March 31, 2013 or during the year ended December 31, 2012.

The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2013 and for the year ended December 31, 2012:

			Gains (Losses) Included in
(In thousands)	Beginning Balance		Earnings			Other Comprehensive Income				Purchases			(Sales)			Maturities			Transfer in		Ending Balance
Three months ended March 31, 2013:
Assets:
Fixed maturities available for sale:
Corporate	$	59,065	$	(15	)	$	144			$	14,297		$	(14,255	)	$	(3,467	)	$	—	$	55,769
Total	59,065		(15		)	144				14,297			(14,255		)	(3,467		)	—		55,769
Equity securities available for sale:
Common stocks	1,408		—			—				—			(170		)	—			—		1,238
Preferred stocks	621		—			(235		)		—			—			—			—		386
Total	2,029		—			(235		)		—			(170		)	—			—		1,624
Arbitrage trading account	928		169			—			—	—		—	—			—			—		1,097
Total	$	62,022	$	154		$	(91	)		$	14,297		$	(14,425	)	$	(3,467	)	$	—	$	58,490
Liabilities:
Securities sold but not yet purchased	$	20	$	(18	)	$	—			$	—		$	—		$	—		$	—	$	2
For the year ended December 31, 2012:
Assets:
Fixed maturities available for sale:
Corporate	$	67,828	$	(1,497	)	$	9,622			$	283		$	—		$	(17,171	)	$	—	$	59,065
Total	67,828		(1,497		)	9,622				283			—			(17,171		)	—		59,065
Equity securities available for sale:
Common stocks	1,559		—			—				—			(151		)	—			—		1,408
Preferred stocks	12,303		1,126			(1,737		)		—			(11,071		)	—			—		621
Total	13,862		1,126			(1,737		)		—			(11,222		)	—			—		2,029
Arbitrage trading account	851		(3,534		)	3,570				—			(52		)	—			93		928
Total	$	82,541	$	(3,905	)	$	11,455			$	283		$	(11,274	)	$	(17,171	)	$	93	$	62,022
Liabilities:
Securities sold but not yet purchased	$	21	$	(1	)	$	—			$	—		$	—		$	—		$	—	$	20

There were no significant transfers in or out of Level 3 during the three months ended March 31, 2013 or during the year ended December 31, 2012.

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Real Estate

3 Months Ended

Mar. 31, 2013

Real Estate [Abstract]

Real Estate [Text Block]

Real Estate

Investment in real estate represents directly owned property held for investment, as follows:    

	Carrying value as of
	March 31,		December 31,
(In thousands)	2013		2012
Properties in operation	$	264,755	$	282,899
Properties under development	324,022		323,836
Total	$	588,777	$	606,735

Properties in operation represent an office building in London and a long-term ground lease in Washington D.C. These properties are net of accumulated depreciation and amortization of $11,397,000 and $10,354,000, as of March 31, 2013 and December 31, 2012, respectively. Related depreciation expense was $1,757,000 and $2,105,000 for the three months ended March 31, 2013 and 2012, respectively. Future minimum rental income expected on operating leases relating to real estate held for investment is $1,099,000 in 2013, $1,504,000 in 2014, $1,549,000 in 2015, $1,596,000 in 2016, $1,644,000 in 2017 and $329,013,000 thereafter.

Properties under development represent an office building in London, a mixed-use project in Washington D.C. and an office complex in New York City. The Company expects to fund further development costs for these projects with a combination of its own funds and external financing.

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Investments In Equity Securities Available for Sale

3 Months Ended

Mar. 31, 2013

Available-for-sale Securities [Abstract]

Investments In Equity Securities Available for Sale

Investments in Equity Securities

At March 31, 2013 and December 31, 2012, investments in equity securities were as follows:

(In thousands)	Cost		Gross Unrealized					Fair Value		Carrying Value
			Gains		Losses
March 31, 2013
Common stocks	$	224,378	$	71,995	$	(1,342	)	$	295,031	$	295,031
Preferred stocks	82,600		23,340		(1,585		)	104,355		104,355
Total	$	306,978	$	95,335	$	(2,927	)	$	399,386	$	399,386
December 31, 2012
Common stocks	$	222,671	$	60,102	$	(707	)	$	282,066	$	282,066
Preferred stocks	85,504		10,103		(1,651		)	93,956		93,956
Total	$	308,175	$	70,205	$	(2,358	)	$	376,022	$	376,022

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Real Estate Real Estate (Details 1) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Investment Holdings [Line Items]
Real Estate Investment Property, Accumulated Depreciation	$ 11,397,000		$ 10,354,000
Real Estate Accumulated Depreciation, Depreciation Expense	1,757,000	2,105,000
Real Estate Funds [Member]
Investment Holdings [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	1,099,000
Operating Leases, Future Minimum Payments Receivable, in Two Years	1,504,000
Operating Leases, Future Minimum Payments Receivable, in Three Years	1,549,000
Operating Leases, Future Minimum Payments Receivable, in Four Years	1,596,000
Operating Leases, Future Minimum Payments Receivable, in Five Years	1,644,000
Operating Leases, Future Minimum Payments Receivable, Thereafter	$ 329,013,000

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Statements of Comprehensive Income (Notes)

3 Months Ended

Mar. 31, 2013

Comprehensive Income [Abstract]

Comprehensive Income (Loss) Note [Text Block]

Statement of Comprehensive Income (Loss)

The following table presents the components of the changes in accumulated other comprehensive income (loss) (AOCI) as of and for the three months ended March 31, 2013:

	Unrealized Investment gains					Currency translation adjustments			Net pension asset					Accumulated other comprehensive income (loss)
(In thousands)
Changes in AOCI
Beginning of period	$	517,658				$	(36,676	)	$	(15,351	)			$	465,631
Other comprehensive income (loss) before reclassifications	20,989					(46,623		)	—					(25,634		)
Amounts reclassified from AOCI	(13,179		)			—			1,814					(11,365		)
Other comprehensive income (loss)	7,810					(46,623		)	1,814					(36,999		)
Unrealized investment gain related to non-controlling interest	(40		)			—			—					(40		)
Ending balance	$	525,428				$	(83,299	)	$	(13,537	)			$	428,592
Amounts reclassified from AOCI
Pre-tax	$	(20,075	)	(1	)	$	—		$	2,792		(3	)	$	(17,283	)
Tax effect	6,896			(2	)	—			(978		)	(2	)	5,918
After-tax amounts reclassified	$	(13,179	)			$	—		$	1,814				$	(11,365	)
Other comprehensive income (loss)
Pre-tax	$	12,015				$	(46,623	)	$	2,792				$	(31,816	)
Tax effect	(4,205		)			—			(978		)			(5,183		)
Other comprehensive income (loss)	$	7,810				$	(46,623	)	$	1,814				$	(36,999	)

_______________

(1) Net investment gains in the consolidated statements of operations.

(2) Income tax expense in the consolidated statements of operations.

(3) Other operating costs and expenses in the consolidated statements of operations.

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Investments In Fixed Maturity Securities

3 Months Ended

Mar. 31, 2013

Investments in Fixed Maturity Securities [Abstract]

Investments In Fixed Maturity Securities

Investments in Fixed Maturity Securities

At March 31, 2013 and December 31, 2012, investments in fixed maturity securities were as follows:

(In thousands)	Amortized Cost		Gross Unrealized					Fair Value		Carrying Value
			Gains		Losses
March 31, 2013
Held to maturity:
State and municipal	$	66,125	$	17,675	$	—		$	83,800	$	66,125
Residential mortgage-backed	31,181		4,977		—			36,158		31,181
Corporate	4,997		555		—			5,552		4,997
Total held to maturity	102,303		23,207		—			125,510		102,303
Available for sale:
U.S. government and government agency	807,341		68,429		(58		)	875,712		875,712
State and municipal	4,110,714		308,121		(9,219		)	4,409,616		4,409,616
Mortgage-backed securities:
Residential (1)	1,293,875		48,550		(6,878		)	1,335,547		1,335,547
Commercial	203,260		6,504		(398		)	209,366		209,366
Corporate	3,370,627		210,832		(10,380		)	3,571,079		3,571,079
Foreign	1,065,472		96,381		(359		)	1,161,494		1,161,494
Total available for sale	10,851,289		738,817		(27,292		)	11,562,814		11,562,814
Total investments in fixed maturity securities	$	10,953,592	$	762,024	$	(27,292	)	$	11,688,324	$	11,665,117
December 31, 2012
Held to maturity:
State and municipal	$	65,190	$	18,529	$	—		$	83,719	$	65,190
Residential mortgage-backed	32,764		5,286		—			38,050		32,764
Corporate	4,997		605		—			5,602		4,997
Total held to maturity	102,951		24,420		—			127,371		102,951
Available for sale:
U.S. government and government agency	827,591		72,532		(1,660		)	898,463		898,463
State and municipal	4,449,238		328,974		(9,693		)	4,768,519		4,768,519
Mortgage-backed securities:
Residential (1)	1,395,739		53,846		(7,456		)	1,442,129		1,442,129
Commercial	268,671		5,641		(744		)	273,568		273,568
Corporate	3,144,480		214,322		(12,083		)	3,346,719		3,346,719
Foreign	1,029,284		83,347		(1,024		)	1,111,607		1,111,607
Total available for sale	11,115,003		758,662		(32,660		)	11,841,005		11,841,005
Total investments in fixed maturity securities	$	11,217,954	$	783,082	$	(32,660	)	$	11,968,376	$	11,943,956

___________

(1) Gross unrealized losses for residential mortgage-backed securities include $1,925,000 and $3,037,000 as of March 31, 2013 and December 31, 2012, respectively, related to the non-credit portion of other-than-temporary impairments (“OTTI”) recognized in other comprehensive income.

The amortized cost and fair value of fixed maturity securities at March 31, 2013, by contractual maturity, are shown below. Actual maturities may differ from contractual maturities because certain issuers may have the right to call or prepay obligations.

(In thousands)	Amortized Cost		Fair Value
Due in one year or less	$	798,683	$	826,292
Due after one year through five years	3,482,465		3,673,747
Due after five years through ten years	2,536,987		2,806,448
Due after ten years	2,607,141		2,800,766
Mortgage-backed securities	1,528,316		1,581,071
Total	$	10,953,592	$	11,688,324

At March 31, 2013, there were no investments, other than investments in United States government and government agency securities, which exceeded 10% of common stockholders’ equity.

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Arbitrage Trading Account And Arbitrage Funds

3 Months Ended

Mar. 31, 2013

Arbitrage Trading Account And Arbitrage Funds [Abstract]

Arbitrage Trading Account And Arbitrage Funds

Arbitrage Trading Account

At March 31, 2013 and December 31, 2012, the fair value and carrying value of the arbitrage trading account were $701 million and $329 million, respectively. The primary focus of the trading account is merger arbitrage. Merger arbitrage is the business of investing in the securities of publicly held companies which are the targets in announced tender offers and mergers. Arbitrage investing differs from other types of investing in its focus on transactions and events believed likely to bring about a change in value over a relatively short time period (usually four months or less). The Company believes that this makes arbitrage investments less vulnerable to changes in general financial market conditions.

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Securities in an Unrealized Loss Position (Securities in an Unrealized Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Less than 12 Months	$ 1,080,605	$ 1,221,105
Gross Unrealized Losses, Less than 12 Months	10,434	11,595
Fair Value, 12 Months or Greater	238,937	315,818
Gross Unrealized Losses, 12 Months or Greater	19,785	23,423
Fair Value, Total	1,319,542	1,536,923
Gross Unrealized Losses, Total	30,219	35,018
U.S. Government And Government Agency [Member]
Fair Value, Less than 12 Months	24,203	69,551
Gross Unrealized Losses, Less than 12 Months	58	1,660
Fair Value, 12 Months or Greater	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fair Value, Total	24,203	69,551
Gross Unrealized Losses, Total	58	1,660
State And Municipal [Member]
Fair Value, Less than 12 Months	133,592	152,694
Gross Unrealized Losses, Less than 12 Months	1,830	1,639
Fair Value, 12 Months or Greater	100,664	135,967
Gross Unrealized Losses, 12 Months or Greater	7,389	8,054
Fair Value, Total	234,256	288,661
Gross Unrealized Losses, Total	9,219	9,693
Mortgage-Backed Securities [Member]
Fair Value, Less than 12 Months	451,452	484,731
Gross Unrealized Losses, Less than 12 Months	4,235	3,629
Fair Value, 12 Months or Greater	44,419	58,292
Gross Unrealized Losses, 12 Months or Greater	3,041	4,571
Fair Value, Total	495,871	543,023
Gross Unrealized Losses, Total	7,276	8,200
Corporate [Member]
Fair Value, Less than 12 Months	348,050	371,781
Gross Unrealized Losses, Less than 12 Months	2,425	2,964
Fair Value, 12 Months or Greater	66,309	70,537
Gross Unrealized Losses, 12 Months or Greater	7,955	9,119
Fair Value, Total	414,359	442,318
Gross Unrealized Losses, Total	10,380	12,083
Foreign [Member]
Fair Value, Less than 12 Months	91,803	95,623
Gross Unrealized Losses, Less than 12 Months	309	996
Fair Value, 12 Months or Greater	3,221	11,210
Gross Unrealized Losses, 12 Months or Greater	50	28
Fair Value, Total	95,024	106,833
Gross Unrealized Losses, Total	359	1,024
Fixed Maturity Securities [Member]
Fair Value, Less than 12 Months	1,049,100	1,174,380
Gross Unrealized Losses, Less than 12 Months	8,857	10,888
Fair Value, 12 Months or Greater	214,613	276,006
Gross Unrealized Losses, 12 Months or Greater	18,435	21,772
Fair Value, Total	1,263,713	1,450,386
Gross Unrealized Losses, Total	27,292	32,660
Common Stock [Member]
Fair Value, Less than 12 Months	31,119	46,725
Gross Unrealized Losses, Less than 12 Months	1,342	707
Fair Value, 12 Months or Greater	0	0
Gross Unrealized Losses, 12 Months or Greater	0	0
Fair Value, Total	31,119	46,725
Gross Unrealized Losses, Total	1,342	707
Preferred Stock [Member]
Fair Value, Less than 12 Months	386	0
Gross Unrealized Losses, Less than 12 Months	235	0
Fair Value, 12 Months or Greater	24,324	39,812
Gross Unrealized Losses, 12 Months or Greater	1,350	1,651
Fair Value, Total	24,710	39,812
Gross Unrealized Losses, Total	1,585	1,651
Equity Securities Available For Sale [Member]
Fair Value, Less than 12 Months	31,505	46,725
Gross Unrealized Losses, Less than 12 Months	1,577	707
Fair Value, 12 Months or Greater	24,324	39,812
Gross Unrealized Losses, 12 Months or Greater	1,350	1,651
Fair Value, Total	55,829	86,537
Gross Unrealized Losses, Total	$ 2,927	$ 2,358

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Securities In An Unrealized Loss Position Securities In An Unrealized Loss Position (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Number of securities	24
Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities	2
Available For Sale Equity Securities Non Investment Grade Continuous Unrealized Loss Position Aggregate Loss	0
Available For Sale Equity Securities Continuous Unrealized Loss Position Fair Value	25
Available For Sale Equity Securities Continuous Unrealized Loss Position Aggregate Loss	2
Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities	2
Available For Sale Equity Securities Continuous Unrealized Loss Position Fair Value	31
Available For Sale Equity Securities Continuous Unrealized Loss Position Aggregate Loss	1
External Credit Rating, Non Investment Grade [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities	1

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Realized and Unrealized Investment Gains (Losses) (Change in Unrealized Gains (Losses) of Available For Sales Securities) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Change in unrealized gains (losses) before income taxes and noncontrolling interests	$ 6,816	$ 34,437
Income tax expense	994	(12,413)
Noncontrolling interests	(40)	(23)
Total change in unrealized gains	7,770	22,001
Fixed Maturities [Member]
Change in unrealized gains (losses) before income taxes and noncontrolling interests	(15,589)	19,422
Non-Credit Portion of OTTI Recognized In Other Comprehensive Income [Member]
Change in unrealized gains (losses) before income taxes and noncontrolling interests	1,112	1,743
Equity Securities Available For Sale [Member]
Change in unrealized gains (losses) before income taxes and noncontrolling interests	24,561	11,595
Investment Funds [Member]
Change in unrealized gains (losses) before income taxes and noncontrolling interests	$ (3,268)	$ 1,677

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Investments In Equity Securities Available For Sale (Tables)

3 Months Ended

Mar. 31, 2013

Available-for-sale Securities [Abstract]

Available-for-sale Securities [Table Text Block]

At March 31, 2013 and December 31, 2012, investments in equity securities were as follows:

(In thousands)	Cost		Gross Unrealized					Fair Value		Carrying Value
			Gains		Losses
March 31, 2013
Common stocks	$	224,378	$	71,995	$	(1,342	)	$	295,031	$	295,031
Preferred stocks	82,600		23,340		(1,585		)	104,355		104,355
Total	$	306,978	$	95,335	$	(2,927	)	$	399,386	$	399,386
December 31, 2012
Common stocks	$	222,671	$	60,102	$	(707	)	$	282,066	$	282,066
Preferred stocks	85,504		10,103		(1,651		)	93,956		93,956
Total	$	308,175	$	70,205	$	(2,358	)	$	376,022	$	376,022

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Statements of Cash Flow (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Supplemental Cash Flow Information [Abstract]
Interest payments	$ 53,691,000	$ 45,358,000
Income taxes paid	$ 23,850,000	$ 3,249,000

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Realized And Unrealized Investment Gains (Losses)

3 Months Ended

Mar. 31, 2013

Realized and Unrealized Investment Gains (Losses) [Abstract]

Realized and Unrealized Investment Gains (Losses)

Realized and Unrealized Investment Gains

Realized and unrealized investment gains and losses are as follows:

	For the Three Months Ended March 31,
(In thousands)	2013			2012
Realized investment gains and losses:
Fixed maturity securities:
Gains	$	10,996		$	14,955
Losses	(5,966		)	(543		)
Equity securities available for sale	15,245			26,238
Investment funds	194			1,310
Other	(500		)	1,517
Total	19,969			43,477
Change in valuation allowance, net other-than-temporary impairments:
Decrease in valuation allowance	—			6,998
Other-than-temporary impairments	—			(2,984		)
Total	—			4,014
Net investment gains	19,969			47,491
Income tax expense	(6,989		)	(16,409		)
Total after-tax investment gains and losses	$	12,980		$	31,082

Change in unrealized investment gains and losses:
Fixed maturity securities	$	(15,589	)	$	19,422
Previously impaired fixed maturity securities	1,112			1,743
Equity securities available for sale	24,561			11,595
Investment funds	(3,268		)	1,677
Total change in unrealized investment gains and losses	6,816			34,437
Income tax benefit (expense)	994			(12,413		)
Noncontrolling interests	(40		)	(23		)
Total after-tax unrealized gains and losses	$	7,770		$	22,001

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Restricted Stock Units

3 Months Ended

Mar. 31, 2013

Restricted Stock Units [Abstract]

Restricted Stock Units

Restricted Stock Units

Pursuant to its stock incentive plan, the Company may issue restricted stock units (RSUs) to employees of the Company and its subsidiaries. The RSUs generally vest five years from the award date and are subject to other vesting and forfeiture provisions contained in the award agreement. RSUs are expensed pro-ratably over the vesting period. RSU expenses were $5 million and $7 million for the three months ended March 31, 2013 and 2012, respectively. Grants of RSUs are made periodically, generally every other year. A summary of RSUs issued in the three months ended March 31,2013 and 2012 follows:

($ in thousands)	Units	Fair Value
Three months ended March 31:
2013	36,450	$	1,515
2012	35,000	$	1,218

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Acquistions (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Current Assets, Marketable Securities	$ 3,911
Business Acquisition, Purchase Price Allocation, Noncurrent Assets	898
Business Acquisition, Purchase Price Allocation, Goodwill Amount	19,664
Acquired Finite-lived Intangible Asset, Amount	44,800
Business Acquisition, Purchase Price Allocation, Other Noncurrent Assets	60,661
Business Acquisition, Purchase Price Allocation, Assets Acquired	129,934
Business Acquisition, Purchase Price Allocation, Notes Payable and Long-term Debt	(27,612)
Business Acquisition, Purchase Price Allocation, Other Noncurrent Liabilities	(17,076)
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net	$ 85,246

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Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value, Assets and Liabilities Measured on Recurring Basis [Abstract]

Assets And Liabilities Measured At Fair value, On A Recurring Basis

The following tables present the assets and liabilities measured at fair value, on a recurring basis, as of March 31, 2013 and December 31, 2012 by Level:

(In thousands)	Total		Level 1		Level 2		Level 3
March 31, 2013
Assets:
Fixed maturity securities available for sale:
U.S. government and agency	$	875,712	$	—	$	875,712	$	—
State and municipal	4,409,616		—		4,409,616		—
Mortgage-backed securities	1,544,913		—		1,544,913		—
Corporate	3,571,079		—		3,515,310		55,769
Foreign	1,161,494		—		1,161,494		—
Total fixed maturity securities available for sale	11,562,814		—		11,507,045		55,769
Equity securities:
Common stocks	295,031		293,793		—		1,238
Preferred stocks	104,355		—		103,969		386
Total equity securities	399,386		293,793		103,969		1,624
Arbitrage trading account	701,223		236,670		463,456		1,097
Total	$	12,663,423	$	530,463	$	12,074,470	$	58,490
Liabilities:
Securities sold but not yet purchased	$	79,965	$	70,580	$	9,383	$	2
December 31, 2012
Assets:
Fixed maturity securities available for sale:
U.S. government and agency	$	898,463	$	—	$	898,463	$	—
State and municipal	4,768,519		—		4,768,519		—
Mortgage-backed securities	1,715,697		—		1,715,697		—
Corporate	3,346,719		—		3,287,654		59,065
Foreign	1,111,607		—		1,111,607		—
Total fixed maturity securities available for sale	11,841,005		—		11,781,940		59,065
Equity securities:
Common stocks	282,066		280,658		—		1,408
Preferred stocks	93,956		—		93,335		621
Total equity securities	376,022		280,658		93,335		2,029
Arbitrage trading account	329,077		233,603		94,546		928
Total	$	12,546,104	$	514,261	$	11,969,821	$	62,022
Liabilities:
Securities sold but not yet purchased	$	121,487	$	114,909	$	6,558	$	20

Summarize Changes In Level 3 Assets

The following tables summarize changes in Level 3 assets and liabilities for the three months ended March 31, 2013 and for the year ended December 31, 2012:

			Gains (Losses) Included in
(In thousands)	Beginning Balance		Earnings			Other Comprehensive Income				Purchases			(Sales)			Maturities			Transfer in		Ending Balance
Three months ended March 31, 2013:
Assets:
Fixed maturities available for sale:
Corporate	$	59,065	$	(15	)	$	144			$	14,297		$	(14,255	)	$	(3,467	)	$	—	$	55,769
Total	59,065		(15		)	144				14,297			(14,255		)	(3,467		)	—		55,769
Equity securities available for sale:
Common stocks	1,408		—			—				—			(170		)	—			—		1,238
Preferred stocks	621		—			(235		)		—			—			—			—		386
Total	2,029		—			(235		)		—			(170		)	—			—		1,624
Arbitrage trading account	928		169			—			—	—		—	—			—			—		1,097
Total	$	62,022	$	154		$	(91	)		$	14,297		$	(14,425	)	$	(3,467	)	$	—	$	58,490
Liabilities:
Securities sold but not yet purchased	$	20	$	(18	)	$	—			$	—		$	—		$	—		$	—	$	2
For the year ended December 31, 2012:
Assets:
Fixed maturities available for sale:
Corporate	$	67,828	$	(1,497	)	$	9,622			$	283		$	—		$	(17,171	)	$	—	$	59,065
Total	67,828		(1,497		)	9,622				283			—			(17,171		)	—		59,065
Equity securities available for sale:
Common stocks	1,559		—			—				—			(151		)	—			—		1,408
Preferred stocks	12,303		1,126			(1,737		)		—			(11,071		)	—			—		621
Total	13,862		1,126			(1,737		)		—			(11,222		)	—			—		2,029
Arbitrage trading account	851		(3,534		)	3,570				—			(52		)	—			93		928
Total	$	82,541	$	(3,905	)	$	11,455			$	283		$	(11,274	)	$	(17,171	)	$	93	$	62,022
Liabilities:
Securities sold but not yet purchased	$	21	$	(1	)	$	—			$	—		$	—		$	—		$	—	$	20

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Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement of Other Comprehensive Income [Abstract]
Net income before noncontrolling interests	$ 116,598	$ 135,232
Other comprehensive income (loss):
Change in unrealized foreign exchange gains (losses)	(46,623)	15,583
Unrealized investment gain related to non-controlling interest	7,810	22,024
Amounts reclassified from AOCI	1,814	824
Other comprehensive income (loss)	(36,999)	38,431
Comprehensive income	79,599	173,663
Comprehensive income (loss), net of Tax, Attributable to noncontrolling interests	(23)	63
Comprehensive income to common stockholders	$ 79,576	$ 173,726

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Recent Accounting Pronouncements

3 Months Ended

Mar. 31, 2013

New Accounting Pronouncements and Changes in Accounting Principles [Abstract]

Recent Accounting Pronouncements

Recent Accounting Pronouncements

In February 2013, the Financial Accounting Standards Board (FASB) issued ASU 2013-02 relating to disclosures about items reclassified out of accumulated other comprehensive income. The Company’s adoption of the updated guidance effective January 1, 2013 resulted in a change in the disclosures for accumulated other comprehensive income in the Company’s consolidated financial statements but did not have any impact on the Company’s results of operations, financial position or liquidity.

All recently issued but not yet effective accounting and reporting standards are either not applicable to the Company or are not expected to have a material impact on the Company.

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Investment Funds Investment Funds (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Investment Holdings [Line Items]
Carrying Value	$ 793,603		$ 809,689
Income (Losses) from Investment Funds	137,941	158,718
Real Estate Funds [Member]
Investment Holdings [Line Items]
Carrying Value	379,006		373,259
Energy Fund [Member]
Investment Holdings [Line Items]
Carrying Value	147,383		146,325
Arbitrage [Member]
Investment Holdings [Line Items]
Carrying Value	63,462		63,920
Other [Member]
Investment Holdings [Line Items]
Carrying Value	203,752		226,185
Investment Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	10,934	27,623
Investment Funds [Member] | Real Estate Funds [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	(2,001)	8,655
Investment Funds [Member] | Energy Fund [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	9,466	17,938
Investment Funds [Member] | Arbitrage [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	(458)	1,770
Investment Funds [Member] | Other [Member]
Investment Holdings [Line Items]
Income (Losses) from Investment Funds	$ 3,927	$ (740)

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Fair Value Measurements (Summarize Changes in Level 3 Assets) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Beginning Balance	$ 62,022	$ 82,541
Earnings	154	(3,905)
Other Comprehensive Income	(91)	11,455
Purchases	14,297	283
(Sales)	(14,425)	(11,274)
Maturities	(3,467)	(17,171)
Transfer out	0	93
Ending Balance	58,490	62,022
Fixed Maturities Securities [Member]
Beginning Balance	59,065	67,828
Earnings	(15)	(1,497)
Other Comprehensive Income	144	9,622
Purchases	14,297	283
(Sales)	(14,255)	0
Maturities	(3,467)	(17,171)
Transfer out	0	0
Ending Balance	55,769	59,065
Equity Securities Available For Sale [Member]
Beginning Balance	2,029	13,862
Earnings	0	1,126
Other Comprehensive Income	(235)	(1,737)
Purchases	0	0
(Sales)	(170)	(11,222)
Maturities	0	0
Transfer out	0	0
Ending Balance	1,624	2,029
Securities Sold But Not Yet Purchased [Member]
Beginning Balance	20	21
Earnings	(18)	(1)
Other Comprehensive Income	0	0
Purchases	0	0
(Sales)	0	0
Maturities	0	0
Transfer out	0	0
Ending Balance	2	20
Corporate [Member] | Fixed Maturities Securities [Member]
Beginning Balance	59,065	67,828
Earnings	(15)	(1,497)
Other Comprehensive Income	144	9,622
Purchases	14,297	283
(Sales)	(14,255)	0
Maturities	(3,467)	(17,171)
Transfer out	0	0
Ending Balance	55,769	59,065
Common Stock [Member] | Equity Securities Available For Sale [Member]
Beginning Balance	1,408	1,559
Earnings	0	0
Other Comprehensive Income	0	0
Purchases	0	0
(Sales)	(170)	151
Maturities	0	0
Transfer out	0	0
Ending Balance	1,238	1,408
Preferred Stock [Member] | Equity Securities Available For Sale [Member]
Beginning Balance	621	12,303
Earnings	0	1,126
Other Comprehensive Income	(235)	(1,737)
Purchases	0	0
(Sales)	0	(11,071)
Maturities	0	0
Transfer out	0	0
Ending Balance	386	621
Arbitrage Trading Account [Member]
Beginning Balance	928	851
Earnings	169	(3,534)
Other Comprehensive Income	0	3,570
Purchases	0	0
(Sales)	0	52
Maturities	0	0
Transfer out	0	93
Ending Balance	$ 1,097	$ 928

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Industry Segments

3 Months Ended

Mar. 31, 2013

Industry Segments Disclosure [Abstract]

Industry Segments

Segments

The Company’s financial results are presented for the following reportable business segments:

• Insurance-Domestic - commercial insurance business, including excess and surplus lines and admitted lines, throughout the United States;

• Insurance-International - insurance business primarily in the United Kingdom, Continental Europe, South America, Canada, Scandinavia, and Australia; and

• Reinsurance-Global - reinsurance business on a facultative and treaty basis, primarily in the United States, United Kingdom, Europe, Australia, and the Asia-Pacific Region.

During the first quarter of 2013, the Company changed the aggregation of its business segments. All domestic insurance operating companies, previously included in the Specialty, Regional and Alternative Markets segments, were aggregated into the Insurance-Domestic segment; all reinsurance operating companies were aggregated into the Reinsurance-Global segment; and all international insurance companies were aggregated into the Insurance-International segment. The segment disclosures for prior periods have been revised to be consistent with the new reportable business segment presentation. The segment disclosures for the years ended December 31, 2012, 2011 and 2010, and as of December 31, 2012 and 2011, have also been included herein, revised for the new reportable business segment presentation.

The accounting policies of the segments are the same as those described in the summary of significant accounting policies. Income tax expense and benefits are calculated based upon the Company’s overall effective tax rate.

Summary financial information about the Company's business segments is presented in the following tables.

	Revenues
(In thousands)	Earned Premiums		Investment Income		Other		Total		Pre-Tax Income (Loss)			Net Income (Loss)
Three months ended March 31, 2013:
Insurance-Domestic	$	884,378	$	97,797	$	26,736	$	1,008,911	$	141,350		$	99,408
Insurance-International	171,119		12,061		—		183,180		22,382			15,477
Reinsurance-Global	176,622		22,499		—		199,121		37,941			26,394
Corporate and eliminations (1)	—		3,572		92,016		95,588		(61,419		)	(37,644		)
Net investment gains	—		—		19,969		19,969		19,969			12,980
Total	$	1,232,119	$	135,929	$	138,721	$	1,506,769	$	160,223		$	116,615
Three months ended March 31, 2012:
Insurance-Domestic	$	810,069	$	112,086	$	23,877	$	946,032	$	147,735		$	105,880
Insurance-International	143,885		10,331		—		154,216		15,699			11,112
Reinsurance-Global	145,697		28,687		—		174,384		31,638			23,086
Corporate and eliminations (1)	—		6,515		50,067		56,582		(55,260		)	(35,842		)
Net investment gains	—		—		47,491		47,491		47,491			31,082
Total	$	1,099,651	$	157,619	$	121,435	$	1,378,705	$	187,303		$	135,318
Twelve months ended December 31, 2012:
Insurance-Domestic	$	3,417,022	$	424,787	$	103,133	$	3,944,942	$	578,500		$	412,514
Insurance-International	631,841		45,796		—		677,637		51,639			37,499
Reinsurance-Global	624,653		106,932		—		731,585		103,690			76,584
Corporate and eliminations (1)	—		9,248		249,677		258,925		(242,366		)	(152,807		)
Net investment gains	—		—		210,465		210,465		210,465			136,802
Total	$	4,673,516	$	586,763	$	563,275	$	5,823,554	$	701,928		$	510,592
Twelve months ended December 31, 2011:
Insurance-Domestic	$	3,121,281	$	372,053	$	92,847	$	3,586,181	$	467,126		$	344,521
Insurance-International	508,509		36,958		—		545,467		36,912			28,054
Reinsurance-Global	531,077		97,795		—		628,872		85,271			66,174
Corporate and eliminations (1)	—		19,545		250,438		269,983		(201,704		)	(129,185		)
Net investment gains	—		—		125,481		125,481		125,481			81,647
Total	$	4,160,867	$	526,351	$	468,766	$	5,155,984	$	513,086		$	391,211
Twelve months ended December 31, 2010:
Insurance-Domestic	$	2,963,486	$	385,783	$	85,417	$	3,434,686	$	589,138		$	425,337
Insurance-International	378,693		29,011		—		407,704		15,172			13,050
Reinsurance-Global	493,403		106,862		—		600,265		134,996			99,492
Corporate and eliminations (1)	—		8,869		215,964		224,833		(196,977		)	(128,348		)
Net investment gains	—		—		56,581		56,581		56,581			36,874
Total	$	3,835,582	$	530,525	$	357,962	$	4,724,069	$	598,910		$	446,405

Identifiable assets by segment are as follows:

(Dollars in thousands)	March 31, 2013		December 31, 2012		December 31, 2011
Insurance-Domestic	$	14,023,370	$	14,661,476	$	13,126,472
Insurance-International	1,690,937		1,605,448		1,341,907
Reinsurance-Global	3,420,508		3,337,937		3,168,528
Corporate and eliminations	985,819		615,118		766,966
Total	$	20,120,634	$	20,155,896	$	18,403,873

___________

(1) Corporate and eliminations represent corporate revenues and expenses that are not allocated to business segments.

Net premiums earned by major line of business are as follows:

	For the Three Months Ended
	March 31,
(In thousands)	2013		2012
Insurance-Domestic
Other liability	$	295,588	$	273,564
Workers’ compensation	229,011		189,544
Short-tail lines (1)	178,749		173,902
Commercial automobile	116,122		110,367
Products liability	64,908		62,692
Total	884,378		810,069
Insurance-International
Other liability	15,218		15,534
Workers’ compensation	22,889		18,618
Short-tail lines (1)	72,123		52,478
Commercial automobile	34,639		30,668
Products liability	26,250		26,587
Total	171,119		143,885
Reinsurance-Global
Casualty	121,327		105,089
Property	55,295		40,608
Total	176,622		145,697
Total	$	1,232,119	$	1,099,651

_____________________

(1) Short-tail lines includes commercial multi-peril (non-liability), inland and ocean marine, accident and health, fidelity and surety, boiler and machinery and other lines.

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Industry Segments (Identifiable Assets by Segment) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Consolidated Assets	$ 20,120,634		$ 20,155,896		$ 18,403,873
Insurance-Domestic Segment [Member] [Domain]
Consolidated Assets	14,023,370		14,661,476		13,126,472
Insurance-International Segment [Member] [Domain]
Consolidated Assets	1,690,937		1,605,448		1,341,907
Reinsurance-Global Segment [Member] [Domain]
Consolidated Assets	3,420,508		3,337,937		3,168,528
Corporate, Other and Eliminations Segment [Member]
Consolidated Assets	$ 985,819	[1]	$ 615,118	[1]	$ 766,966	[1]

[1] Corporate and eliminations represent corporate revenues and expenses that are not allocated to business segments.

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Loans Receivable Loans Receivable, Net (Tables)

3 Months Ended

Mar. 31, 2013

Loans Receivable [Abstract]

Schedule of Loans Receivable

Loans receivable are as follows:

(In thousands)	March 31, 2013		December 31, 2012
Loans receivable	$	456,533	$	401,961
Valuation allowance:
Specific	$	3,500	$	3,000
General	2,682		2,620
Total	$	6,182	$	5,620
Impaired loans:
With a specific valuation allowance	$	3,003	$	1,775
Without a valuation allowance	30,000		31,023
Unpaid principal balance	36,003		35,872
	For the Three Months Ended March 31,
	2013		2012
Increase (decrease) in valuation allowance	$	62	$	(6,896	)
Loans receivable charged off	463		85

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Loans Receivable

3 Months Ended

Mar. 31, 2013

Loans Receivable, Net [Abstract]

Loans Receivable

Loans Receivable

Loans receivable are as follows:

(In thousands)	March 31, 2013		December 31, 2012
Loans receivable	$	456,533	$	401,961
Valuation allowance:
Specific	$	3,500	$	3,000
General	2,682		2,620
Total	$	6,182	$	5,620
Impaired loans:
With a specific valuation allowance	$	3,003	$	1,775
Without a valuation allowance	30,000		31,023
Unpaid principal balance	36,003		35,872
	For the Three Months Ended March 31,
	2013		2012
Increase (decrease) in valuation allowance	$	62	$	(6,896	)
Loans receivable charged off	463		85

Loans receivable in non-accrual status were $3 million at both March 31, 2013 and December 31, 2012. If these loans had been current, additional interest income of $0.7 million and $0.2 million would have been recognized in accordance with their original terms for the three months ended March 31, 2013 and 2012, respectively.

The Company monitors the performance of its loans receivable and assesses the ability of the borrower to pay principal and interest based upon loan structure, underlying property values, cash flow and related financial and operating performance of the property and market conditions. Loans receivable with a potential for default are further assessed using discounted cash flow analysis and comparable cost and sales methodologies, if appropriate.

The Company's six largest loans receivable, which have an aggregate amortized cost of $243 million and an aggregate fair value of $250 million at March 31, 2013, are secured by commercial real estate located primarily in New York City, California, Hawaii and Chicago. These loans earn interest at floating LIBOR-based interest rates and have maturities (inclusive of extension options) through August 2025.

The Company utilizes an internal risk rating system to assign a risk to each of its commercial loans. The loan rating system takes into consideration credit quality indicators including loan to value ratios, which compare the outstanding loan amount to the estimated value of the property, the borrower's financial condition and performance with respect to loan terms, the Company's position in the capital structure, and the overall leverage in the capital structure. Based on this rating system, one loan with an aggregate cost basis of $30 million was considered to be impaired at March 31, 2013. A determination was made as to the amount of loss in the event of a default and whether the loss is probable. The results of the determination were considered in connection with the valuation allowance noted above.