Repurchase Agreements - Amounts At Risk (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
[CitigroupMember]
Repurchase Agreement Counterparties With Whom Amount At Risk Exceeds Ten Percent of Stockholders Equity [Line Items]
Amount At Risk	$ 6,075	$ 3,714
Weighted Average Maturity of Repurchase Agreement in Days	18 days	18 days
[SouthStreetMember]
Repurchase Agreement Counterparties With Whom Amount At Risk Exceeds Ten Percent of Stockholders Equity [Line Items]
Amount At Risk		$ 1,802
Weighted Average Maturity of Repurchase Agreement in Days		7 days