Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net income	$ 43,099	$ 16,544	$ 27,806
Adjustments to reconcile net income to cash provided by operating activities:
Decrease (increase) in accrued interest receivable	2,368	(1,607)	546
Increase (decrease) in accrued interest payable	1,413	(204)	(600)
Loss on derivative instruments, net	5,606	43,128	53,393
Loss (gain) on sale of investments, net	(4,238)	(978)	16,223
Fair value adjustments, net	(103)	(69)	(208)
Amortization of investment premiums, net	150,729	152,308	137,837
Other amortization and depreciation, net	1,502	5,338	8,900
Stock-based compensation expense	2,709	2,965	2,719
Other operating activities	(1,047)	(2,430)	306
Net cash and cash equivalents provided by operating activities	210,514	216,951	214,476
Investing activities:
Purchase of investments	(435,046)	(1,122,970)	(599,381)
Principal payments received on investments	448,567	494,275	518,303
Proceeds from sales of investments	99,284	449,921	503,918
Principal payments received on mortgage loans held for investment, net	4,953	15,570	16,787
Payment to acquire interest in limited partnership	0	(6,000)	(4,000)
Distributions received from limited partnership	10,835	0	0
Net payments on derivatives, including terminations	(60,588)	(39,929)	(11,415)
Other investing activities	(37)	(237)	(7)
Net cash and cash equivalents provided by (used in) investing activities	67,968	(209,370)	424,205
Financing activities:
Borrowings under repurchase agreements and FHLB advances	40,594,639	23,555,007	22,547,991
Repayments of repurchase agreement borrowings and FHLB advances	(40,805,107)	(23,458,697)	(23,115,878)
Principal payments on non-recourse collateralized financing	(2,039)	(2,395)	(2,167)
Decrease (increase) in restricted cash	26,421	(8,927)	(28,878)
Proceeds from issuance of preferred stock	548	0	0
Proceeds from issuance of common stock	137	166	252
Cash paid for stock issuance costs	(201)	0	0
Cash paid for repurchases of common stock	(310)	(41,171)	0
Payments related to tax withholding for stock-based compensation	(485)	(557)	(507)
Dividends paid	(51,900)	(61,016)	(64,880)
Net cash and cash equivalents used in financing activities	(238,297)	(17,590)	(664,067)
Net increase (decrease) in cash and cash equivalents	40,185	(10,009)	(25,386)
Cash and cash equivalents at beginning of period	33,935	43,944	69,330
Cash and cash equivalents at end of period	74,120	33,935	43,944
Supplemental Disclosure of Cash Activity:
Cash paid for interest	$ 24,033	$ 19,260	$ 19,445