Derivative Financial Instruments (Details 2) (USD $)	9 Months Ended			9 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended					9 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 RMBS item	Dec. 31, 2011 RMBS	Sep. 30, 2012 RMBS Minimum	Sep. 30, 2012 RMBS Maximum	Sep. 30, 2012 RMBS Weighted average	Sep. 30, 2012 Non-Qualifying Basis Swaps	Dec. 31, 2011 Non-Qualifying Basis Swaps	Sep. 30, 2012 Non-Qualifying Basis Swaps / Caps	Sep. 30, 2011 Non-Qualifying Basis Swaps / Caps	Sep. 30, 2012 Non-Qualifying Basis Swaps / Caps	Sep. 30, 2011 Non-Qualifying Basis Swaps / Caps	Sep. 30, 2012 Non-Qualifying Basis Swaps / Caps Interest Expense	Sep. 30, 2011 Non-Qualifying Basis Swaps / Caps Interest Expense	Sep. 30, 2012 Non-Qualifying Forward Contracts	Sep. 30, 2012 Non-Qualifying Forward Contracts Other Income	Sep. 30, 2012 Qualifying	Sep. 30, 2012 Qualifying Interest Rate Swaps / Caps	Sep. 30, 2011 Qualifying Interest Rate Swaps / Caps	Sep. 30, 2012 Terminated hedges Interest Rate Swaps	Dec. 31, 2011 Terminated hedges Interest Rate Swaps	Sep. 30, 2012 Terminated hedges Interest Rate Swaps / Caps	Sep. 30, 2011 Terminated hedges Interest Rate Swaps / Caps	Sep. 30, 2012 Terminated hedges Interest Rate Swaps / Caps	Sep. 30, 2011 Terminated hedges Interest Rate Swaps / Caps	Sep. 30, 2011 Terminated hedges Interest Rate Swaps / Caps Maximum
Derivative Financial Instruments
Change in fair value				$ 100,000							$ (400,000)	$ 400,000	$ (1,200,000)	$ (200,000)
Interest expense expected to be reclassified from qualifying cash flow hedges over the next twelve months																			(14,500,000)
Number of investments purchased				8
Investments purchased	65,542,970	4,618,943		52,200,000
Percentage of finance to individual investment						80.00%	90.00%
Amount of repurchase agreement for financing the purchase of investments				46,100,000
Variable interest rate, description				LIBOR
Variable rate, spread (as a percent)						1.25%	1.75%
Total principal paydowns	44,046,864	1,039,119		4,800,000
Debt paid down due to principal paydowns received				3,000,000
Net interest income				500,000
Net deferred loss in accumulated other comprehensive loss																						2,400,000	2,900,000
Additional interest expense related to the amortization of the loss																								200,000	400,000	700,000	1,300,000
Reduction to interest expense related to the accretion of the net gains																								100,000		200,000	200,000	100,000
Amount of net deferred loss expected to be recorded to interest expense over the next twelve months																								700,000		700,000
Fair Value, classified in Other Assets				47,400,000					405,000	1,563,000							4,473,000
Repurchase financing				43,000,000
Fixed interest rate (as a percent)								5.67%
Stated maturity period (in years)				26 years 3 months 18 days
Estimated remaining life (in years)				5 years
Net fair value	52,217,641		29,994,214	51,489,857	29,256,791
Amount of Loss Recognized in Other Comprehensive Loss (Effective Portion)																				7,507,000	19,559,000
Amount of Loss Reclassified from Accumulated Other Comprehensive Loss into Interest Expense (Effective Portion)																				(12,883,000)	(20,918,000)
Amount of Gain (Loss) Recognized in income															50,000	152,000		65,000
Cumulative amount of other comprehensive loss related to net unrealized losses on derivatives designated as qualifying hedges	(43,500,000)		(48,800,000)
Cumulative amount of other comprehensive loss related to net unrealized losses on derivatives designated as cash flow hedges attributable to fair value of qualifying cash flow hedges	(41,100,000)		(45,900,000)
Cumulative amount of other comprehensive loss related to net unrealized losses on derivatives designated as cash flow hedges attributable to deferred losses terminated interest swaps	(3,000,000)		(3,700,000)
Cumulative amount of other comprehensive loss related to net unrealized losses on derivatives designated as cash flow hedges attributable to deferred gains on terminated interest swaps	600,000		800,000
Fair value of derivatives in a net liability position	(20,500,000)		(22,000,000)
Collateral posted	$ 20,800,000		$ 21,900,000