Investments (Details 6) (USD $)	3 Months Ended							12 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Investments
Other invested assets				$ 283,032,000				$ 222,869,000	$ 283,032,000
Other income	(7,600,000)	28,800,000	42,200,000	32,700,000	33,800,000	(13,500,000)	(12,900,000)	63,349,000	40,107,000	58,518,000
Portfolio Funding Company LLC I
Investments
Other invested assets				87,100,000				45,000,000	87,100,000
Equity interest acquired (as a percent)					50.00%			50.00%
Subordinated debt and working capital facility provided as part of loss mitigation efforts				37,800,000				37,800,000	37,800,000
Assets Acquired in Refinancing Transactions
Investments
Other invested assets				129,400,000				107,100,000	129,400,000
Accretable yield on securitized loans				137,100,000				140,900,000	137,100,000
Other income								$ 5,100,000	$ 6,700,000	$ 3,200,000