Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets
Fixed maturities, trading securities, at fair value (amortized cost: 2012, $13,653,615; 2011, $13,394,404)	$ 14,395,315	$ 13,941,829
Short-term investments, trading securities, at fair value (amortized cost: 2012, $150,634; 2011, $42,563)	150,552	42,571
Equities, trading securities, at fair value (cost: 2012, $1,000,326; 2011, $917,613)	1,094,002	944,691
Other invested assets	333,361	358,154
Total investments	15,973,230	15,287,245
Funds held - directly managed (cost: 2012, $895,261; 2011, $1,241,222)	930,741	1,268,010
Cash and cash equivalents, at fair value, which approximates amortized cost	1,121,705	1,342,257
Accrued investment income	184,315	189,074
Reinsurance balances receivable	1,991,991	2,059,976
Reinsurance recoverable on paid and unpaid losses	348,086	397,788
Funds held by reinsured companies	805,489	796,290
Deferred acquisition costs	568,391	547,202
Deposit assets	257,208	241,513
Net tax assets	25,098	66,574
Goodwill	456,380	455,533
Intangible assets	214,270	133,867
Other assets	103,528	70,044
Total assets	22,980,432	22,855,373
Liabilities
Unpaid losses and loss expenses	10,709,371	11,273,091
Policy benefits for life and annuity contracts	1,813,244	1,645,662
Unearned premiums	1,534,625	1,448,841
Other reinsurance balances payable	238,578	443,873
Deposit liabilities	252,217	249,382
Net tax liabilities	387,647	297,153
Accounts payable, accrued expenses and other	290,265	208,840
Debt related to senior notes	750,000	750,000
Debt related to capital efficient notes	70,989	70,989
Total liabilities	16,046,936	16,387,831
Shareholders' Equity
Common shares (par value $1.00; issued: 2012, 85,459,905 shares; 2011, 84,766,693 shares)	85,460	84,767
Preferred shares (par value $1.00; issued and outstanding: 2012 and 2011, 35,750,000 shares; aggregate liquidation value: 2012 and 2011, $893,750)	35,750	35,750
Additional paid-in capital	3,861,844	3,803,796
Accumulated other comprehensive income (loss)	10,597	(12,644)
Retained earnings	4,952,002	4,035,103
Common shares held in treasury, at cost (2012, 26,550,530 shares; 2011, 19,444,365 shares)	(2,012,157)	(1,479,230)
Total shareholders' equity	6,933,496	6,467,542
Total liabilities and shareholders' equity	$ 22,980,432	$ 22,855,373