Repurchase Agreements (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	$ 3,564,128	$ 2,093,793
Debt, Weighted Average Interest Rate	0.70%	0.61%
Deferred Costs	(659)
Fair value of Collateral Pledged	3,935,504	2,268,312
Weighted Average Maturity of Agreements	67 days	57 days
Line of Credit Facility, Amount Outstanding	196,520
Line of Credit Facility, Maximum Borrowing Capacity	200,000
Line of Credit Facility, Interest Rate at Period End	1.47%
Agency RMBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	2,365,982	1,447,508
Debt, Weighted Average Interest Rate	0.48%	0.38%
Fair value of Collateral Pledged	2,458,200	1,521,107
Agency CMBS and CMBS IO [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	692,311	290,362
Debt, Weighted Average Interest Rate	0.95%	0.59%
Fair value of Collateral Pledged	856,939	329,612
Non-Agency RMBS [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	7,808	12,195
Debt, Weighted Average Interest Rate	1.84%	1.85%
Fair value of Collateral Pledged	9,634	13,597
Non-Agency CMBS and CMBS IO [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	470,573	283,266
Debt, Weighted Average Interest Rate	1.36%	1.54%
Fair value of Collateral Pledged	579,248	336,124
Bonds [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Transfers Accounted for as Secured Borrowings, Associated Liabilities, Carrying Amount	28,113	60,462
Debt, Weighted Average Interest Rate	1.64%	1.65%
Fair value of Collateral Pledged	$ 31,483	$ 67,872