Investments (Tables)

12 Months Ended

Dec. 31, 2011

Investments [Abstract]

Schedule Of Available For Sale Securities

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
December 31, 2011
U.S. Government and Government agencies	$	31,309	$	2,321	$	—		$	33,630
States, municipalities and political subdivisions		29,128		4,351		—			33,479
Corporate debt:
Financial institutions		17,431		348		(292	)		17,487
Industrials		73,539		4,268		—			77,807
Utilities		74,990		6,623		—			81,613
Total fixed maturity investments, available for sale	$	226,397	$	17,911	$	(292	)	$	244,016
December 31, 2010
U.S. Government and Government agencies	$	85,030	$	6,923	$	—		$	91,953
Non-U.S. Government and Government agencies		138,386		9,539		(2,541	)		145,384
States, municipalities and political subdivisions		107,289		10,901		(13	)		118,177
Corporate debt:
Financial institutions		66,660		6,776		(38	)		73,398
Industrials		310,664		20,548		(2	)		331,210
Utilities		120,515		11,212		—			131,727
Total fixed maturity investments, available for sale	$	828,544	$	65,899	$	(2,594	)	$	891,849

Schedule Of Trading Securities

	December 31, 2011				December 31, 2010
	Fair Value		Amortized Cost		Fair Value		Amortized Cost
U.S. Government and Government agencies	$	1,278,265	$	1,263,948	$	1,229,720	$	1,219,233
Non-U.S. Government and Government agencies		256,756		251,784		120,793		115,969
States, municipalities and political subdivisions		133,902		128,633		127,436		128,995
Corporate debt:
Financial institutions		1,161,904		1,174,308		1,261,219		1,247,895
Industrials		987,006		974,731		627,524		629,360
Utilities		105,564		103,262		101,472		101,622
Residential mortgage-backed:
Non-agency residential		302,827		314,077		371,935		340,545
Agency residential		1,183,893		1,156,913		1,195,905		1,200,430
Commercial mortgage-backed		331,371		326,697		184,043		184,380
Asset-backed		513,198		513,638		549,050		545,893
Total fixed maturity investments, trading	$	6,254,686	$	6,207,991	$	5,769,097	$	5,714,322
	December 31, 2011				December 31, 2010
	Fair Value		Original Cost		Fair Value		Original Cost
Equity securities	$	367,483	$	356,370	$	174,976	$	160,513
Other invested assets (1)		540,409		529,851		347,632		331,772
	$	907,892	$	886,221	$	522,608	$	492,285

(1) Within the Company's financial statements and footnotes "other invested assets" include the Company's investments in both hedge funds and private equity funds.

Schedule Of Contractual Maturity Dates Of Available For Sale Fixed Maturity Investments

	December 31, 2011
	Amortized Cost		Fair Value
Due within one year	$	31,492	$	31,981
Due after one year through five years		164,329		176,592
Due after five years through ten years		27,561		31,634
Due after ten years		3,015		3,809
	$	226,397	$	244,016

Schedule Of Fair Value Of Investments And Cash And Cash Equivalents

Fund Type	Fair Value as of December 31, 2011		Unfunded Commitments		Long Exposure(1) (%  of funded)			Short Exposure(2) (% of funded)			Gross Exposure(3)			Net Exposure(4)
Private equity (primary and secondary)	$	83,787	$	111,566		100	%		0	%		100	%		100	%
Mezzanine debt		14,535		100,344		100	%		0	%		100	%		100	%
Distressed		10,543		33,968		100	%		0	%		100	%		100	%
Total private equity		108,865		245,878
Distressed		42,849		—		61	%		31	%		92	%		30	%
Equity long/short		159,615		—		75	%		49	%		124	%		26	%
Multi-strategy		157,251		—		98	%		20	%		118	%		78	%
Event driven		71,829		—		81	%		66	%		147	%		15	%
Total hedge funds		431,544		—
Total other invested assets	$	540,409	$	245,878

(1) Long exposure represents the ratio of the fund's long investments in securities to the fund's equity capital (over 100% may denote explicit borrowing). Four of the Company's hedge funds, two multi-strategy funds, one event driven fund and one equity long/short fund had long exposure greater than 100% of the funds' net asset value (indicating explicit leverage). The funds had long exposure of 145%, 103%, 139% and 103%, respectively, as of December 31, 2011.

(2) Short exposure represents the ratio of the fund's equity to securities sold short.

(3) Gross exposure is the addition of the long and short exposures.

(4) Net exposure is the subtraction of the short exposure from the long exposure.  

Schedule Of Net Investment Income

	For the year ended December 31,
	2011			2010			2009
Fixed maturity investments	$	194,093		$	245,407		$	306,578
Equity securities and other invested assets		15,088			9,800			1,506
Cash and cash equivalents		963			671			1,570
Expenses		(14,196	)		(11,735	)		(8,979	)
Net investment income	$	195,948		$	244,143		$	300,675

Components Of Realized Gains And Losses

f)  Components of Realized Gains and Losses Components of realized gains and losses are summarized in the following table:
	For the year ended December 31,
	2011			2010			2009
Gross realized gains on sale of invested assets	$	154,941		$	242,421		$	185,322
Gross realized losses on sale of invested assets		(62,169	)		(26,621	)		(90,856	)
Treasury yield hedge		—			(3,958	)		—
Futures not designated as hedges		(57,234	)		—			—
Foreign exchange forwards not designated as hedges		(2,807	)		—			—
Mark-to-market changes: debt securities trading		(8,078	)		42,172			12,603
Mark-to-market changes: foreign exchange forwards and futures not designated as hedges		(5,924	)		—			—
Mark-to-market changes: put options		(4,125	)		—			—
Mark-to-market changes: other invested assets and equity securities		(4,527	)		29,738			19,283
Gain on sale of Program Administrator		—			1,860			—
Net realized investment gains	$	10,077		$	285,612		$	126,352
Proceeds from sale of available for sale securities	$	646,479		$	2,703,695		$	8,402,666
Proceeds from sale of trading securities		6,841,666			11,042,968			1,870,625

Schedule Of Company's Trust Accounts On Deposit, Outstanding And Remaining Letter Of Credit Facilities, And Collateral Committed To Support The Letter Of Credit Facilities

	As of December 31, 2011		As of December 31, 2010
Total trust accounts on deposit	$	2,029,138	$	1,657,441
Total letter of credit facilities:
Citibank Europe plc		900,000		900,000
Credit Facility		800,000		800,000
Total letter of credit facilities		1,700,000		1,700,000
Total letter of credit facilities outstanding:
Citibank Europe plc		675,636		689,851
Credit Facility		141,351		158,983
Total letter of credit facilities outstanding		816,987		848,834
Total letter of credit facilities remaining:
Citibank Europe plc		224,364		210,149
Credit Facility(1)		658,649		641,017
Total letter of credit facilities remaining		883,013		851,166
Collateral committed to support the letter of credit facilities	$	1,044,236	$	1,121,345

(1) Net of any borrowing or repayments under the Unsecured Facility (as defined in Note 9). See Note 9 for further details on the Unsecured Facility.

Summary Of The Market Value Of Those Available For Sale Investments In An Unrealized Loss Position For Periods Less Than And Greater Than 12 Months

	December 31, 2011					December 31, 2010
	Gross Fair		Unrealized			Gross Fair		Unrealized
	Value		Loss			Value		Loss
Less than 12 months
Non-U.S. Government and Government agencies	$	—	$	—		$	34,204	$	(1,116	)
States, municipalities and political subdivisions		—		—			472		(13	)
Corporate debt
Financial institutions		9,440		(292	)		2,796		(38	)
Industrials		—		—			2,150		(2	)
	$	9,440	$	(292	)	$	39,622	$	(1,169	)
More than 12 months
Non-U.S. Government and Government agencies	$	—	$	—		$	10,998	$	(1,425	)
	$	—	$	—		$	10,998	$	(1,425	)
	$	9,440	$	(292	)	$	50,620	$	(2,594	)

Range Of Credit Default Rates And Severity Rates

Significant Input	Range of Inputs	Weighted Average of Input
Credit default rate	0.6%—11.0%	6.1%
Severity rate	30.1%—100.0%	37.2%

Schedule Of Amounts Related To Credit Losses On Debt Securities For Which A Portion Of The OTTI Was Recognized In Other Comprehensive Income

	For the Year Ended December 31, 2010
Beginning balance of credit losses	$	1,096
Additions for credit loss for which OTTI was not previously recognized		168
Reductions for securities sold during the period (realized)		—
Reductions for OTTI previously recognized due to intent to sell		—
Additions resulting from the increase in credit losses		—
Reductions resulting from the improvement in expected cash flows		—
Adoption of ASU 2010-11		(1,264	)
Ending balance of credit losses	$	—

Net Impairment Charges Recognized In Earnings

	2011		2010		2009
Asset backed	$	—	$	—	$	31,545
Mortgage backed		—		168		18,027
U.S. government and government agencies		—		—		5
Non-U.S. government and government agencies		—		—		—
Corporate		—		—		—
States, municipalities and political subdivisions		—		—		—
Total other-than-temporary impairment charges	$	—	$	168	$	49,577