Consolidated Statements Of Operations And Comprehensive Income (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
REVENUES:
Gross premiums written	$ 497,052	$ 504,420	$ 646,870	$ 680,929	$ 416,537	$ 442,698	$ 519,598	$ 560,688	$ 2,329,271	$ 1,939,521	$ 1,758,397
Premiums ceded	(134,429)	(112,883)	(152,160)	(91,976)	(109,705)	(92,438)	(123,795)	(79,817)	(491,448)	(405,755)	(365,942)
Net premiums written	362,623	391,537	494,710	588,953	306,832	350,260	395,803	480,871	1,837,823	1,533,766	1,392,455
Change in unearned premiums	113,621	49,480	(64,963)	(187,063)	88,637	21,080	(40,496)	(145,995)	(88,925)	(76,774)	(32,907)
Net premiums earned	476,244	441,017	429,747	401,890	395,469	371,340	355,307	334,876	1,748,898	1,456,992	1,359,548
Net investment income	38,360	39,121	42,451	47,209	45,489	47,883	52,368	50,208	167,141	195,948	244,143
Net realized investment gains	14,379	149,813	8,663	133,581	31,632	(130,809)	58,878	50,376	306,436	10,077	285,612
Net impairment charges recognized in earnings									0	0	(168)
Other income									0	101,744	913
Total revenues	528,983	629,951	480,861	582,680	539,334	323,414	466,553	435,460	2,222,475	1,764,761	1,890,048
EXPENSES:
Net losses and loss expenses	414,734	258,948	240,380	225,202	213,345	205,546	235,813	304,452	1,139,264	959,156	707,883
Acquisition costs	55,910	51,086	51,588	47,138	46,562	39,680	42,971	38,082	205,722	167,295	159,489
General and administrative expenses	84,404	78,572	73,979	70,366	70,492	66,007	67,201	67,956	307,321	271,656	286,557
Amortization of intangible assets	633	633	634	633	678	767	766	767	2,533	2,978	3,483
Interest expense	13,826	13,822	14,001	13,756	13,754	13,748	13,745	13,742	55,405	54,989	40,242
Foreign exchange loss	860	1,023	(1,019)	(81)	(549)	2,966	1,184	(442)	783	3,159	444
Total expenses	570,367	404,084	379,563	357,014	344,282	328,714	361,680	424,557	1,711,028	1,459,233	1,198,098
Income before income taxes	(41,384)	225,867	101,298	225,666	195,052	(5,300)	104,873	10,903	511,447	305,528	691,950
Income tax expense	(237)	6,220	4,947	7,510	11,952	5,672	11,073	2,283	18,440	30,980	26,945
NET INCOME	(41,147)	219,647	96,351	218,156	183,100	(10,972)	93,800	8,620	493,007	274,548	665,005
Other comprehensive loss:
Unrealized (losses) gains on investments arising during the year net of applicable deferred income tax (benefit) expense 2012: $(265); 2011: $3,035; 2010: $10,209									(493)	5,243	162,653
Reclassification adjustment for net realized investment gains included in net income, net of applicable income tax									(13,991)	(47,894)	(213,478)
Other comprehensive loss									(14,484)	(42,651)	(50,825)
COMPREHENSIVE INCOME									$ 478,523	$ 231,897	$ 614,180
PER SHARE DATA
Basic earnings per share	$ (1.17)	$ 6.16	$ 2.66	$ 5.86	$ 4.80	$ (0.29)	$ 2.45	$ 0.23	$ 13.67	$ 7.21	$ 14.30
Diluted earnings per share	$ (1.17)	$ 6.00	$ 2.59	$ 5.70	$ 4.63	$ (0.29)	$ 2.36	$ 0.21	$ 13.30	$ 6.92	$ 13.32
Weighted average common shares outstanding	35,097,043	35,652,768	36,288,596	37,205,166	38,138,558	38,110,368	38,346,489	38,199,867	36,057,145	38,093,351	46,491,279
Weighted average common shares and common share equivalents outstanding	35,097,043	36,616,734	37,189,722	38,284,635	39,524,273	38,110,368	39,800,753	40,383,523	37,069,885	39,667,905	49,913,317
Dividends paid per share									$ 1.875	$ 0.750	$ 1.050