Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities:
Net income	$ 16,544	$ 27,806	$ 68,069
Adjustments to reconcile net income to cash provided by operating activities:
Decrease in accrued interest receivable	(1,607)	546	1,370
Decrease in accrued interest payable	(204)	(600)	(347)
Loss on derivative instruments, net	43,128	53,393	10,076
Loss (gain) on sale of investments, net	978	(16,223)	(3,354)
Fair value adjustments, net	(69)	(208)	652
Amortization of investment premiums, net	152,308	137,837	128,865
Other amortization and depreciation	5,338	8,900	7,743
Stock-based compensation expense	2,965	2,719	2,314
Other operating activities	(2,393)	381	(6,628)
Net cash and cash equivalents provided by operating activities	216,988	214,551	208,760
Investing activities:
Purchase of investments	(1,122,970)	(599,381)	(1,419,060)
Principal payments received on investments	494,275	518,303	913,210
Proceeds from sales of investments	449,921	503,918	358,090
Principal payments received on mortgage loans held for investment, net	15,570	16,787	15,828
Payment to acquire interest in limited partnership	(6,000)	(4,000)	0
Net payments on derivatives, including terminations	(39,929)	(11,415)	(39,097)
Other investing activities	(237)	(7)	5,891
Net cash and cash equivalents (used in) provided by investing activities	(209,370)	424,205	(165,138)
Financing activities:
Borrowings under repurchase agreements and FHLB advances	23,555,007	22,547,991	29,176,511
Repayments of repurchase agreement borrowings and FHLB advances	(23,458,697)	(23,115,878)	(29,160,302)
Principal payments on non-recourse collateralized financing	(2,395)	(2,167)	(17,840)
Increase in restricted cash	(8,927)	(28,878)	(13,346)
Proceeds from issuance of preferred stock	0	0	54,251
Proceeds from issuance of common stock, net of issuance costs	129	177	7,436
Cash paid for repurchases of common stock	(41,171)	0	(6,934)
Payments related to tax withholding for share-based compensation	(557)	(507)	(545)
Dividends paid	(61,016)	(64,880)	(69,332)
Net cash and cash equivalents provided by (used in) financing activities	(17,627)	(664,142)	(30,101)
Net decrease in cash and cash equivalents	(10,009)	(25,386)	13,521
Cash and cash equivalents at beginning of period	43,944	69,330	55,809
Cash and cash equivalents at end of period	33,935	43,944	69,330
Supplemental Disclosure of Cash Activities:
Cash paid for interest	$ 19,260	$ 19,445	$ 33,517