Schedule of Reverse Repurchase Agreements by Maturity (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2016	Dec. 31, 2015
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements	[1]	$ 1,149,064	$ 1,174,189
Debt, Weighted Average Interest Rate		1.09%	0.97%
Remaining Days to Maturity, Reverse Repurchase Agreements		79 days	100 days
Agency residential mortgage-backed securities [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 893,758	$ 933,320
Debt, Weighted Average Interest Rate		0.67%	0.58%
Remaining Days to Maturity, Reverse Repurchase Agreements		39 days	56 days
Agency residential mortgage-backed securities [Member] | Maturity up to 30 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 420,442	$ 295,277
Debt, Weighted Average Interest Rate		0.61%	0.54%
Remaining Days to Maturity, Reverse Repurchase Agreements		14 days	14 days
Agency residential mortgage-backed securities [Member] | Maturity 31 to 60 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 319,396	$ 203,144
Debt, Weighted Average Interest Rate		0.70%	0.54%
Remaining Days to Maturity, Reverse Repurchase Agreements		43 days	44 days
Agency residential mortgage-backed securities [Member] | Maturity 61 to 90 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 117,846	$ 239,431
Debt, Weighted Average Interest Rate		0.77%	0.68%
Remaining Days to Maturity, Reverse Repurchase Agreements		75 days	74 days
Agency residential mortgage-backed securities [Member] | Maturity 91 to 120 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 0	$ 193,962
Debt, Weighted Average Interest Rate		0.00%	0.56%
Remaining Days to Maturity, Reverse Repurchase Agreements		0 days	106 days
Agency residential mortgage-backed securities [Member] | Maturity 151 to 180 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 36,074	$ 1,506
Debt, Weighted Average Interest Rate		0.82%	1.57%
Remaining Days to Maturity, Reverse Repurchase Agreements		167 days	175 days
Credit Portfolio [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 241,641	$ 240,869
Debt, Weighted Average Interest Rate		2.70%	2.47%
Remaining Days to Maturity, Reverse Repurchase Agreements		230 days	272 days
Credit Portfolio [Member] | Maturity up to 30 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 19,044	$ 14,674
Debt, Weighted Average Interest Rate		2.23%	1.94%
Remaining Days to Maturity, Reverse Repurchase Agreements		17 days	17 days
Credit Portfolio [Member] | Maturity 31 to 60 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 19,620	$ 26,419
Debt, Weighted Average Interest Rate		2.08%	1.87%
Remaining Days to Maturity, Reverse Repurchase Agreements		33 days	39 days
Credit Portfolio [Member] | Maturity 61 to 90 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 89,927	$ 82,292
Debt, Weighted Average Interest Rate		2.61%	2.46%
Remaining Days to Maturity, Reverse Repurchase Agreements		70 days	67 days
Credit Portfolio [Member] | Maturity 91 to 120 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 2,478	$ 0
Debt, Weighted Average Interest Rate		2.47%	0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements		116 days	0 days
Credit Portfolio [Member] | Maturity 151 to 180 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 2,912	$ 24,193
Debt, Weighted Average Interest Rate		2.29%	2.62%
Remaining Days to Maturity, Reverse Repurchase Agreements		168 days	164 days
Credit Portfolio [Member] | Maturity 181 to 360 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 61,114	$ 23,877
Debt, Weighted Average Interest Rate		3.06%	2.80%
Remaining Days to Maturity, Reverse Repurchase Agreements		334 days	346 days
Credit Portfolio [Member] | Maturity greater than 360 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 46,546	$ 69,414
Debt, Weighted Average Interest Rate		2.69%	2.51%
Remaining Days to Maturity, Reverse Repurchase Agreements		575 days	666 days
US Treasury Securities [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 13,665	$ 0
Debt, Weighted Average Interest Rate		0.27%	0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements		1 day	0 days
US Treasury Securities [Member] | Maturity up to 30 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 13,665	$ 0
Debt, Weighted Average Interest Rate		0.27%	0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements		1 day	0 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.