Schedule of Reverse Repurchase Agreements by Maturity (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2017	Dec. 31, 2016
Borrowings [Line Items]
Reverse repurchase agreements	[1]	$ 1,086,271	$ 1,033,581
Debt, Weighted Average Interest Rate		1.33%	1.32%
Remaining Days to Maturity, Reverse Repurchase Agreements		59 days	56 days
Agency residential mortgage-backed securities [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 793,020	$ 790,312
Debt, Weighted Average Interest Rate		0.97%	0.89%
Remaining Days to Maturity, Reverse Repurchase Agreements		46 days	41 days
Agency residential mortgage-backed securities [Member] | Maturity up to 30 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 384,009	$ 405,725
Debt, Weighted Average Interest Rate		0.93%	0.83%
Remaining Days to Maturity, Reverse Repurchase Agreements		13 days	18 days
Agency residential mortgage-backed securities [Member] | Maturity 31 to 60 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 169,346	$ 195,288
Debt, Weighted Average Interest Rate		0.92%	0.94%
Remaining Days to Maturity, Reverse Repurchase Agreements		42 days	45 days
Agency residential mortgage-backed securities [Member] | Maturity 61 to 90 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 134,491	$ 149,965
Debt, Weighted Average Interest Rate		1.12%	0.97%
Remaining Days to Maturity, Reverse Repurchase Agreements		75 days	74 days
Agency residential mortgage-backed securities [Member] | Maturity 91 to 120 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 1,752	$ 8,240
Debt, Weighted Average Interest Rate		1.04%	0.83%
Remaining Days to Maturity, Reverse Repurchase Agreements		104 days	102 days
Agency residential mortgage-backed securities [Member] | Maturity 121 to 150 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 83,680	$ 11,798
Debt, Weighted Average Interest Rate		0.99%	0.96%
Remaining Days to Maturity, Reverse Repurchase Agreements		137 days	131 days
Agency residential mortgage-backed securities [Member] | Maturity 151 to 180 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 19,742	$ 19,296
Debt, Weighted Average Interest Rate		1.15%	1.05%
Remaining Days to Maturity, Reverse Repurchase Agreements		166 days	164 days
Credit Portfolio [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 256,759	$ 237,841
Debt, Weighted Average Interest Rate		2.47%	2.75%
Remaining Days to Maturity, Reverse Repurchase Agreements		106 days	105 days
Credit Portfolio [Member] | Maturity up to 30 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 82,992	$ 94,849
Debt, Weighted Average Interest Rate		1.57%	2.55%
Remaining Days to Maturity, Reverse Repurchase Agreements		5 days	16 days
Credit Portfolio [Member] | Maturity 31 to 60 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 18,374	$ 26,974
Debt, Weighted Average Interest Rate		2.07%	2.36%
Remaining Days to Maturity, Reverse Repurchase Agreements		41 days	47 days
Credit Portfolio [Member] | Maturity 61 to 90 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 61,625	$ 41,522
Debt, Weighted Average Interest Rate		2.75%	2.43%
Remaining Days to Maturity, Reverse Repurchase Agreements		79 days	77 days
Credit Portfolio [Member] | Maturity 91 to 120 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 1,235	$ 10,084
Debt, Weighted Average Interest Rate		2.89%	2.91%
Remaining Days to Maturity, Reverse Repurchase Agreements		118 days	97 days
Credit Portfolio [Member] | Maturity 121 to 150 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 0	$ 1,239
Debt, Weighted Average Interest Rate		0.00%	2.73%
Remaining Days to Maturity, Reverse Repurchase Agreements		0 days	124 days
Credit Portfolio [Member] | Maturity 151 to 180 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 14,794	$ 12,616
Debt, Weighted Average Interest Rate		3.29%	3.17%
Remaining Days to Maturity, Reverse Repurchase Agreements		164 days	165 days
Credit Portfolio [Member] | Maturity 181 to 360 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 77,739	$ 50,557
Debt, Weighted Average Interest Rate		3.13%	3.46%
Remaining Days to Maturity, Reverse Repurchase Agreements		240 days	316 days
US Treasury Securities [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 36,492	$ 5,428
Debt, Weighted Average Interest Rate		1.06%	0.91%
Remaining Days to Maturity, Reverse Repurchase Agreements		3 days	4 days
US Treasury Securities [Member] | Maturity up to 30 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 36,492	$ 5,428
Debt, Weighted Average Interest Rate		1.06%	0.91%
Remaining Days to Maturity, Reverse Repurchase Agreements		3 days	4 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.