Schedule of Reverse Repurchase Agreements by Maturity (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2016	Dec. 31, 2015
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements	[1]	$ 983,814	$ 1,174,189
Debt, Weighted Average Interest Rate		1.11%	0.97%
Remaining Days to Maturity, Reverse Repurchase Agreements		63 days	100 days
Agency residential mortgage-backed securities [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 770,138	$ 933,320
Debt, Weighted Average Interest Rate		0.72%	0.58%
Remaining Days to Maturity, Reverse Repurchase Agreements		35 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		$ 448,489	$ 295,277
Debt, Weighted Average Interest Rate		0.71%	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		$ 197,704	$ 203,144
Debt, Weighted Average Interest Rate		0.71%	0.54%
Remaining Days to Maturity, Reverse Repurchase Agreements		45 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		$ 85,050	$ 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		$ 14,709	$ 193,962
Debt, Weighted Average Interest Rate		0.75%	0.56%
Remaining Days to Maturity, Reverse Repurchase Agreements		110 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		$ 24,186	$ 1,506
Debt, Weighted Average Interest Rate		0.82%	1.57%
Remaining Days to Maturity, Reverse Repurchase Agreements		164 days	175 days
Credit Portfolio [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 197,925	$ 240,869
Debt, Weighted Average Interest Rate		2.65%	2.47%
Remaining Days to Maturity, Reverse Repurchase Agreements		177 days	272 days
Credit Portfolio [Member] | Maturity up to 30 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 30,386	$ 14,674
Debt, Weighted Average Interest Rate		1.05%	1.94%
Remaining Days to Maturity, Reverse Repurchase Agreements		5 days	17 days
Credit Portfolio [Member] | Maturity 31 to 60 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 38,541	$ 26,419
Debt, Weighted Average Interest Rate		2.20%	1.87%
Remaining Days to Maturity, Reverse Repurchase Agreements		45 days	39 days
Credit Portfolio [Member] | Maturity 61 to 90 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 22,240	$ 82,292
Debt, Weighted Average Interest Rate		2.77%	2.46%
Remaining Days to Maturity, Reverse Repurchase Agreements		81 days	67 days
Credit Portfolio [Member] | Maturity 91 to 120 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 20,301	$ 0
Debt, Weighted Average Interest Rate		3.50%	0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements		119 days	0 days
Credit Portfolio [Member] | Maturity 121 to 150 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 1,406	$ 0
Debt, Weighted Average Interest Rate		2.64%	0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements		129 days	0 days
Credit Portfolio [Member] | Maturity 151 to 180 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 10,119	$ 24,193
Debt, Weighted Average Interest Rate		3.05%	2.62%
Remaining Days to Maturity, Reverse Repurchase Agreements		165 days	164 days
Credit Portfolio [Member] | Maturity 181 to 360 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 11,723	$ 23,877
Debt, Weighted Average Interest Rate		2.99%	2.80%
Remaining Days to Maturity, Reverse Repurchase Agreements		310 days	346 days
Credit Portfolio [Member] | Maturity greater than 360 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 63,209	$ 69,414
Debt, Weighted Average Interest Rate		3.25%	2.51%
Remaining Days to Maturity, Reverse Repurchase Agreements		372 days	666 days
US Treasury Securities [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 15,751	$ 0
Debt, Weighted Average Interest Rate		1.11%	0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements		3 days	0 days
US Treasury Securities [Member] | Maturity up to 30 days [Member]
Repurchase Agreements and Securitized Debt [Line Items]
Reverse repurchase agreements		$ 15,751	$ 0
Debt, Weighted Average Interest Rate		1.11%	0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements		3 days	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.