Schedule of Reverse Repurchase Agreements by Maturity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements	$ 1,396,112	[1]	$ 1,669,433	[1]
Debt, Weighted Average Interest Rate	0.75%		0.65%
Remaining Days to Maturity, Reverse Repurchase Agreements	102 days		105 days
Maturity up to 30 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements	503,021		715,194
Debt, Weighted Average Interest Rate	0.41%		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	336,857		322,874
Debt, Weighted Average Interest Rate	0.67%		0.52%
Remaining Days to Maturity, Reverse Repurchase Agreements	45 days		44 days
Maturity 61 to 90 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements	281,189		289,276
Debt, Weighted Average Interest Rate	0.52%		0.52%
Remaining Days to Maturity, Reverse Repurchase Agreements	73 days		71 days
Maturity 91 to 120 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements	22,413		0
Debt, Weighted Average Interest Rate	0.56%		0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements	105 days		0 days
Maturity 121 to 150 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements	0		21,236
Debt, Weighted Average Interest Rate	0.00%		2.03%
Remaining Days to Maturity, Reverse Repurchase Agreements	0 days		139 days
Maturity 151 to 180 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements	87,741		123,484
Debt, Weighted Average Interest Rate	1.11%		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	23,503		47,768
Debt, Weighted Average Interest Rate	0.47%		0.85%
Remaining Days to Maturity, Reverse Repurchase Agreements	227 days		274 days
Maturity greater than 360 days [Member]
Reverse Repurchase Agreements [Line Items]
Reverse repurchase agreements	$ 141,388		$ 149,601
Debt, Weighted Average Interest Rate	2.43%		2.41%
Remaining Days to Maturity, Reverse Repurchase Agreements	541 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.