Losses and Loss Expense Reserve (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Sample	Jun. 30, 2011	Dec. 31, 2011
Losses and Loss Expense Reserve (Textual) [Abstract]
Net change in loss reserves			$ 771,838		$ 1,671,734
Total net loss expense reserves	138,419		138,419		86,171
Total loss and loss expenses	741,411	196,398	739,091	1,116,045
Reinsurance recoveries of losses included in loss and loss expenses	9,334	17,051	21,852	24,742
Loss reserves ceded to reinsurers	162,948		162,948		153,480
Subrogation recoveries	2,770,191		2,770,191		2,720,266
Subrogation recoveries, net of reinsurance	2,741,210		2,741,210		2,692,414
Subrogation recoveries included in subrogation recoverable	805,121		805,121		829,469
Loss and loss expense reserves included in subrogation recoverable	$ 1,965,070		$ 1,965,070		$ 1,890,797
Number of transaction removed from the Adverse Sample subrogation population			1