Schedule of Reverse Repurchase Agreements by Maturity (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Borrowings [Line Items]
Reverse repurchase agreements	[1]	$ 1,209,315	$ 1,033,581
Debt, Weighted Average Interest Rate		1.98%	1.32%
Remaining Days to Maturity, Reverse Repurchase Agreements		99 days	56 days
Agency residential mortgage-backed securities [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 829,624	$ 790,312
Debt, Weighted Average Interest Rate		1.51%	0.89%
Remaining Days to Maturity, Reverse Repurchase Agreements		44 days	41 days
Agency residential mortgage-backed securities [Member] | Maturity up to 30 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 287,014	$ 405,725
Debt, Weighted Average Interest Rate		1.43%	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		$ 264,058	$ 195,288
Debt, Weighted Average Interest Rate		1.47%	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		$ 277,950	$ 149,965
Debt, Weighted Average Interest Rate		1.63%	0.97%
Remaining Days to Maturity, Reverse Repurchase Agreements		74 days	74 days
Agency residential mortgage-backed securities [Member] | Maturity 91 to 120 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 0	$ 8,240
Debt, Weighted Average Interest Rate		0.00%	0.83%
Remaining Days to Maturity, Reverse Repurchase Agreements		0 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		$ 602	$ 19,296
Debt, Weighted Average Interest Rate		2.56%	1.05%
Remaining Days to Maturity, Reverse Repurchase Agreements		158 days	164 days
US Treasury Securities [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 297	$ 5,428
Debt, Weighted Average Interest Rate		1.70%	0.91%
Remaining Days to Maturity, Reverse Repurchase Agreements		2 days	4 days
US Treasury Securities [Member] | Maturity up to 30 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 297	$ 5,428
Debt, Weighted Average Interest Rate		1.70%	0.91%
Remaining Days to Maturity, Reverse Repurchase Agreements		2 days	4 days
Credit [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 379,394	$ 237,841
Debt, Weighted Average Interest Rate		3.00%	2.75%
Remaining Days to Maturity, Reverse Repurchase Agreements		219 days	105 days
Credit [Member] | Maturity up to 30 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 37,433	$ 94,849
Debt, Weighted Average Interest Rate		2.61%	2.55%
Remaining Days to Maturity, Reverse Repurchase Agreements		13 days	16 days
Credit [Member] | Maturity 31 to 60 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 132,201	$ 26,974
Debt, Weighted Average Interest Rate		2.44%	2.36%
Remaining Days to Maturity, Reverse Repurchase Agreements		49 days	47 days
Credit [Member] | Maturity 61 to 90 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 130,875	$ 41,522
Debt, Weighted Average Interest Rate		2.75%	2.43%
Remaining Days to Maturity, Reverse Repurchase Agreements		77 days	77 days
Credit [Member] | Maturity 91 to 120 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 0	$ 10,084
Debt, Weighted Average Interest Rate		0.00%	2.91%
Remaining Days to Maturity, Reverse Repurchase Agreements		0 days	97 days
Credit [Member] | Maturity 121 to 150 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 8,551	$ 1,239
Debt, Weighted Average Interest Rate		3.79%	2.73%
Remaining Days to Maturity, Reverse Repurchase Agreements		128 days	124 days
Credit [Member] | Maturity 151 to 180 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 8,300	$ 12,616
Debt, Weighted Average Interest Rate		3.40%	3.17%
Remaining Days to Maturity, Reverse Repurchase Agreements		164 days	165 days
Credit [Member] | Maturity 181 to 360 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 5,090	$ 50,557
Debt, Weighted Average Interest Rate		3.59%	3.46%
Remaining Days to Maturity, Reverse Repurchase Agreements		280 days	316 days
Credit [Member] | Maturity greater than 360 days [Member]
Borrowings [Line Items]
Reverse repurchase agreements		$ 56,944	$ 0
Debt, Weighted Average Interest Rate		4.94%	0.00%
Remaining Days to Maturity, Reverse Repurchase Agreements		1094 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.