Investment Securities (Details 2) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended			3 Months Ended
	Sep. 30, 2012 Mortgage-backed securities	Sep. 30, 2013 Mortgage-backed securities security	Dec. 31, 2012 Mortgage-backed securities	Dec. 31, 2012 CMBS	Sep. 30, 2013 RMBS	Sep. 30, 2012 RMBS	Sep. 30, 2013 RMBS	Sep. 30, 2012 RMBS	Dec. 31, 2012 RMBS	Sep. 30, 2013 CMBS excluding securities elected as fair value option	Sep. 30, 2013 CMBS, fair value option	Mar. 31, 2013 Securities, held to maturity
Mortgage-Backed Securities Available-for-Sale
Portion of securities with variable rate					$ 275,400,000		$ 275,400,000		$ 281,200,000
Portion of securities with variable rate (as a percent)				79.60%	87.10%		87.10%		84.40%	1.50%	0.00%
Description of variable rate basis		one-month LIBOR	one-month LIBOR	LIBOR			LIBOR		LIBOR
Description of variable rate basis												one-month LIBOR
Variable rate, weighted average spread (as a percent)				2.30%			0.37%		0.38%			10.00%
Maximum investment in available-for-sale securities with aggregate expected modified durations of less than 12 months (as a percent)							10.00%
Cost of third party management					300,000	700,000	1,700,000	1,500,000
Estimated Fair Value
Securities with a loss less than 12 months		45,304,000	4,096,000		45,304,000		45,304,000		4,096,000
Securities with a loss greater than 12 months		1,604,000	599,000		1,604,000		1,604,000		599,000
Unrealized Losses
Securities with a loss less than 12 months		(2,874,000)	(654,000)		(2,874,000)		(2,874,000)		(654,000)
Securities with a loss greater than 12 months		(519,000)	(37,000)		(519,000)		(519,000)		(37,000)
Number of securities with unrealized loss position		11
Number of securities with recognized other-than-temporary impairment charge		2
Other-than-temporary impairment charge recognized relating to security		86,000
Credit losses included in other-than-temporary impairment charges recognized relating to security	700,000	52,000
Origination of preferred equity interest in limited liability company mandatory redemption												$ 37,200,000