Derivative Instruments (Narrative) (Details) (USD $)				3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2013 Interest Rate Swaps [Member]	Dec. 31, 2012 Interest Rate Swaps [Member]	Jun. 30, 2013 TBAs [Member]	Jun. 30, 2013 TBAs [Member] Short [Member]	Jun. 30, 2013 TBAs [Member] Short [Member]	Jun. 30, 2013 TBAs [Member] Long [Member]	Jun. 30, 2013 TBAs [Member] Long [Member]
Derivative [Line Items]
Notional amount of contracts paired off and sold				$ 388,000,000	$ 473,000,000
Realized gains (losses) on sale of derivative				900,000	800,000
Unrealized gains (losses) recognized				(4,100,000)	(3,700,000)	(1,400,000)	(1,400,000)
Cash pledged as collateral against interest rate swaps which the Company has a right to reclaim	$ 1,000,000	$ 2,400,000	$ 5,200,000