Fair Value of Financial Instruments Level 3 (Details) (Fair Value, Measurements, Recurring [Member], Fair Value, Inputs, Level 3 [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Non-Agency CMBS [Member]	Dec. 31, 2011 Non-Agency CMBS [Member]	Dec. 31, 2012 Non-Agency RMBS [Member]	Dec. 31, 2011 Non-Agency RMBS [Member]	Dec. 31, 2012 Other Investments [Member]	Dec. 31, 2011 Other Investments [Member]	Dec. 31, 2010 Other Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at the beginning of the year	$ 134,024	$ 156,002	$ 123,703	$ 146,670	$ 10,296	$ 9,307	$ 25	$ 25	$ 25
Purchases	7,500	10,054	0	3,054	7,500	7,000
Sales		(3,706)		0		(3,706)
Transfers out to Level 2	(4,670)		(4,670)		0
(Loss) gain recognized in net income		(59)		0		(59)
Unrealized (loss) gain included in other comprehensive income	27	(2,178)	(59)	(2,194)	86	16
Principal payments	(31,241)	(24,930)	(18,437)	(22,652)	(12,804)	(2,278)
Amortization	(395)	(1,159)	(435)	(1,175)	40	16
Balance at the end of the year	$ 105,245	$ 134,024	$ 100,102	$ 123,703	$ 5,118	$ 10,296	$ 25	$ 25	$ 25