Repurchase Agreements (Details 3) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Credit Suisse
Repurchase agreements counterparty risk
Amount at Risk	$ 593,219
Weighted Average Months to Maturity for Repurchase Agreements	1 month
Counterparty risk as percent of Stockholders' Equity, minimum	18.30%
UBS
Repurchase agreements counterparty risk
Amount at Risk	305,865
Weighted Average Months to Maturity for Repurchase Agreements	32 months
Counterparty risk as percent of Stockholders' Equity, minimum	9.40%
UBS AG
Repurchase agreements counterparty risk
Amount at Risk	297,700
UBS Securities LLC
Repurchase agreements counterparty risk
Amount at Risk	8,200
Wells Fargo
Repurchase agreements counterparty risk
Amount at Risk	268,430
Weighted Average Months to Maturity for Repurchase Agreements	18 months
Counterparty risk as percent of Stockholders' Equity, minimum	8.30%
Wells Fargo Bank
Repurchase agreements counterparty risk
Amount at Risk	184,000
Wells Fargo Securities LLC
Repurchase agreements counterparty risk
Amount at Risk	84,400
Deutsche Bank Securities, Inc.
Repurchase agreements counterparty risk
Amount at Risk	$ 214,607
Weighted Average Months to Maturity for Repurchase Agreements	1 month
Counterparty risk as percent of Stockholders' Equity, minimum	6.60%