Schedule of Reverse Repurchase Agreements by Maturity (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2017	Dec. 31, 2016
Borrowings [Line Items]
Reverse repurchase agreements	[1]	$ 1,119,238	$ 1,033,581
Debt, Weighted Average Interest Rate		1.65%	1.32%
Remaining Days to Maturity, Reverse Repurchase Agreements		67 days	56 days
Agency residential mortgage-backed securities [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 791,083	$ 790,312
Debt, Weighted Average Interest Rate		1.20%	0.89%
Remaining Days to Maturity, Reverse Repurchase Agreements		52 days	41 days
Agency residential mortgage-backed securities [Member] | Maturity up to 30 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 218,251	$ 405,725
Debt, Weighted Average Interest Rate		1.15%	0.83%
Remaining Days to Maturity, Reverse Repurchase Agreements		15 days	18 days
Agency residential mortgage-backed securities [Member] | Maturity 31 to 60 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 296,200	$ 195,288
Debt, Weighted Average Interest Rate		1.18%	0.94%
Remaining Days to Maturity, Reverse Repurchase Agreements		46 days	45 days
Agency residential mortgage-backed securities [Member] | Maturity 61 to 90 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 160,959	$ 149,965
Debt, Weighted Average Interest Rate		1.33%	0.97%
Remaining Days to Maturity, Reverse Repurchase Agreements		76 days	74 days
Agency residential mortgage-backed securities [Member] | Maturity 91 to 120 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 114,972	$ 8,240
Debt, Weighted Average Interest Rate		1.17%	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		$ 0	$ 11,798
Debt, Weighted Average Interest Rate		0.00%	0.96%
Remaining Days to Maturity, Reverse Repurchase Agreements		0 days	131 days
Agency residential mortgage-backed securities [Member] | Maturity 151 to 180 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 701	$ 19,296
Debt, Weighted Average Interest Rate		2.27%	1.05%
Remaining Days to Maturity, Reverse Repurchase Agreements		160 days	164 days
Credit Portfolio [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 301,061	$ 237,841
Debt, Weighted Average Interest Rate		2.86%	2.75%
Remaining Days to Maturity, Reverse Repurchase Agreements		112 days	105 days
Credit Portfolio [Member] | Maturity up to 30 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 66,501	$ 94,849
Debt, Weighted Average Interest Rate		1.70%	2.55%
Remaining Days to Maturity, Reverse Repurchase Agreements		4 days	16 days
Credit Portfolio [Member] | Maturity 31 to 60 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 35,808	$ 26,974
Debt, Weighted Average Interest Rate		2.29%	2.36%
Remaining Days to Maturity, Reverse Repurchase Agreements		46 days	47 days
Credit Portfolio [Member] | Maturity 61 to 90 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 71,938	$ 41,522
Debt, Weighted Average Interest Rate		2.60%	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		$ 7,099	$ 10,084
Debt, Weighted Average Interest Rate		2.94%	2.91%
Remaining Days to Maturity, Reverse Repurchase Agreements		97 days	97 days
Credit Portfolio [Member] | Maturity 121 to 150 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 6,709	$ 1,239
Debt, Weighted Average Interest Rate		3.60%	2.73%
Remaining Days to Maturity, Reverse Repurchase Agreements		139 days	124 days
Credit Portfolio [Member] | Maturity 151 to 180 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 9,664	$ 12,616
Debt, Weighted Average Interest Rate		3.56%	3.17%
Remaining Days to Maturity, Reverse Repurchase Agreements		166 days	165 days
Credit Portfolio [Member] | Maturity 181 to 360 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 103,342	$ 50,557
Debt, Weighted Average Interest Rate		3.87%	3.46%
Remaining Days to Maturity, Reverse Repurchase Agreements		222 days	316 days
US Treasury Securities [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 27,094	$ 5,428
Debt, Weighted Average Interest Rate		1.23%	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		$ 27,094	$ 5,428
Debt, Weighted Average Interest Rate		1.23%	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.