Schedule 3 Supplementary Insurance Information (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
U.S. Property & Casualty
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	$ 41,245	$ 32,084	$ 32,515
Future policy benefits, losses, claims and loss expenses	687,332	698,569	781,422
Unearned premiums	367,484	352,155	355,729
Premium revenue	333,410	339,513	379,439
Benefits, claims, losses and settlement expenses	201,017	191,108	201,311
Amortization of deferred policy acquisition costs	48,494	44,750	56,710
Other operating expenses	61,261	57,845	57,633
Premium written	367,296	328,821	382,807
Professional Liability
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	24,468	21,747	22,596
Future policy benefits, losses, claims and loss expenses	1,698,239	1,568,189	1,447,810
Unearned premiums	318,092	355,728	376,176
Premium revenue	410,816	425,226	444,534
Benefits, claims, losses and settlement expenses	328,503	265,465	276,558
Amortization of deferred policy acquisition costs	27,286	38,808	34,323
Other operating expenses	31,742	35,715	25,401
Premium written	412,262	401,562	447,080
Accident & Health
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	5,595	6,019	5,482
Future policy benefits, losses, claims and loss expenses	290,703	264,289	274,010
Unearned premiums	17,065	18,803	17,474
Premium revenue	803,462	760,034	741,539
Benefits, claims, losses and settlement expenses	586,210	556,848	540,917
Amortization of deferred policy acquisition costs	87,639	88,911	87,759
Other operating expenses	33,599	28,359	29,423
Premium written	801,731	761,373	744,554
U.S. Surety & Credit
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	45,917	48,681	45,445
Future policy benefits, losses, claims and loss expenses	107,975	82,738	102,534
Unearned premiums	128,496	127,519	116,307
Premium revenue	210,535	199,908	182,627
Benefits, claims, losses and settlement expenses	52,206	52,940	54,618
Amortization of deferred policy acquisition costs	79,084	77,964	71,552
Other operating expenses	34,836	31,717	26,963
Premium written	208,859	209,373	189,208
International
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	38,502	32,132	31,393
Future policy benefits, losses, claims and loss expenses	643,845	546,077	510,853
Unearned premiums	199,801	191,455	177,550
Premium revenue	368,748	316,186	256,122
Benefits, claims, losses and settlement expenses	233,879	143,412	94,550
Amortization of deferred policy acquisition costs	87,419	72,165	55,948
Other operating expenses	49,227	48,712	59,301
Premium written	391,819	324,344	253,060
Investing
Supplementary Insurance Information, by Segment [Line Items]
Net investment income	212,271	203,819	191,965
Corporate & Other
Supplementary Insurance Information, by Segment [Line Items]
Deferred policy acquisition costs	(483)	(442)	(563)
Future policy benefits, losses, claims and loss expenses	291,284	370,405	436,993
Unearned premiums	96	217	1,511
Premium revenue	199	1,057	32,974
Benefits, claims, losses and settlement expenses	(2,568)	3,256	47,805
Amortization of deferred policy acquisition costs	(1,788)	(552)	2,262
Other operating expenses	57,883	53,656	60,767
Premium written	$ 191	$ 724	$ 29,580