Subsequent Events (Details) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended	1 Months Ended	9 Months Ended		1 Months Ended		1 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2011 Dividend declared	Nov. 03, 2011 Shares repurchased	Sep. 30, 2011 Shares repurchased	Nov. 04, 2011 Shares repurchased	Nov. 30, 2011 CMBS Second Wells Repurchase Agreement Second Wells Repurchase Amendment Y	Nov. 03, 2011 CMBS Second Wells Repurchase Agreement Second Wells Repurchase Amendment	Nov. 30, 2011 Mezzanine Loans Second Wells Repurchase Agreement Second Wells Repurchase Amendment Y	Nov. 03, 2011 Mezzanine Loans Second Wells Repurchase Agreement Second Wells Repurchase Amendment	Nov. 03, 2011 Second Wells Repurchase Agreement Second Wells Repurchase Amendment	Sep. 30, 2011 Second Wells Repurchase Agreement
Subsequent Events
Dividend declared per common stock (in dollars per share)	$ 0.44	$ 0.33	$ 1.30	$ 0.80	$ 0.44
Additional shares purchased (in shares)							283,850
Shares repurchased (in shares)	342,000		342,000					625,850
Aggregate cost of repurchased shares			$ 5,981,000			$ 10,600,000	$ 4,700,000
Weighted-average share cost of repurchased shares (in dollars per share)			$ 17.49			$ 17.00	$ 16.42
Maximum financings available under the Asset Repurchase Agreement													$ 550,000,000	$ 350,000,000
Period of extension of the asset repurchase agreement (in years)									1		2
Maximum liability guaranteed (as a percent)										25.00%
Maximum liability guaranteed, low end of range (as a percent)												25.00%
Maximum liability guaranteed, high end of range (as a percent)												100.00%