Derivative Instruments (Schedule of Information Related to Derivative Instruments) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Notional amount	$ 273,425,000	$ 32,600,000
Interest Rate Swaps [Member]
Derivative [Line Items]
Notional amount	169,425,000	32,600,000
TBAs [Member]
Derivative [Line Items]
Notional amount	104,000,000
Notional amount of contracts paired off and sold	$ 60,000,000