Schedule of Reverse Repurchase Agreements by Maturity (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2015	Dec. 31, 2014
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements	[1]	$ 1,360,408	$ 1,669,433
Debt, Weighted Average Interest Rate		0.76%	0.65%
Remaining Days to Maturity, Reverse Repurchase Agreements		132 days	105 days
Maturity up to 30 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements		$ 163,608	$ 715,194
Debt, Weighted Average Interest Rate		0.70%	0.22%
Remaining Days to Maturity, Reverse Repurchase Agreements		16 days	14 days
Maturity 31 to 60 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements		$ 140,488	$ 322,874
Debt, Weighted Average Interest Rate		0.65%	0.52%
Remaining Days to Maturity, Reverse Repurchase Agreements		47 days	44 days
Maturity 61 to 90 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements		$ 260,762	$ 289,276
Debt, Weighted Average Interest Rate		0.57%	0.52%
Remaining Days to Maturity, Reverse Repurchase Agreements		76 days	71 days
Maturity 91 to 120 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements		$ 206,113	$ 0
Debt, Weighted Average Interest Rate		0.47%	0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements		107 days
Maturity 121 to 150 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements		$ 145,900	$ 21,236
Debt, Weighted Average Interest Rate		0.49%	2.03%
Remaining Days to Maturity, Reverse Repurchase Agreements		136 days	139 days
Maturity 151 to 180 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements		$ 312,866	$ 123,484
Debt, Weighted Average Interest Rate		0.59%	1.25%
Remaining Days to Maturity, Reverse Repurchase Agreements		164 days	162 days
Maturity 181 to 360 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements		$ 21,143	$ 47,768
Debt, Weighted Average Interest Rate		2.54%	0.85%
Remaining Days to Maturity, Reverse Repurchase Agreements		347 days	274 days
Maturity greater than 360 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements		$ 109,528	$ 149,601
Debt, Weighted Average Interest Rate		2.44%	2.41%
Remaining Days to Maturity, Reverse Repurchase Agreements		450 days	631 days

[1] In the Company's Consolidated Statement of Assets, Liabilities, and Equity, all balances associated with repurchase agreements, reverse repurchase agreements, and financial derivatives are presented on a gross basis.