Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Agency Securities, net of amortization of premium and fees	$ 87,407	$ 102,134	$ 113,438	$ 79,832	$ 61,542	$ 56,787	$ 47,809	$ 52,253	$ 382,811		$ 218,391		$ 196,301
Debt securities, trading					508	457	430	624
Interest expense- repurchase agreements	(59,454)	(80,293)	(87,504)	(60,978)	(46,147)	(40,359)	(35,706)	(32,018)	(288,229)		(154,230)		(94,558)
Net Interest Income	41,062	35,606	40,856	33,812	30,407	32,275	30,085	36,151	151,336		128,918		159,875
Realized gain (loss) on sale of Agency Securities (reclassified from Other comprehensive income (loss))	7,996	4,569	(44)	(2,910)	(63,895)	(31,136)	(25,316)	(32,603)	9,611		(152,950)		(8,486)
Other than temporary impairment of Agency Securities (reclassified from Other comprehensive income (loss))					0	0	0	(12,090)	0		(12,090)		(13,707)
Debt securities, trading					27	(84)	(8,884)	2,576
Realized gain (loss) on derivatives	(13,799)	(85,076)	(92,990)	(22,131)	1,709	3,739	(14,341)	(38,604)	(213,996)	[1]	(47,497)	[1]	(22,675)	[1]
Unrealized gain (loss) on derivatives	80,399	3,845	(107,304)	(113,067)	(147,108)	54,169	45,054	97,201	(136,127)		49,316		39,272
Expenses	(8,627)	(10,321)	(10,012)	(9,520)	(8,854)	(9,354)	(9,352)	(9,465)	(38,480)		(37,025)		(35,831)
Net Income (Loss)	108,681	(60,955)	(183,250)	(114,381)	(211,979)	47,704	13,562	44,747	(249,905)		(105,966)		181,154
Dividends on preferred stock	(3,691)	(3,410)	(4,274)	(4,259)	(4,261)	(4,259)	(4,259)	(4,253)	(15,634)		(17,032)		(15,880)
Net Income (Loss) available (related) to common stockholders	$ 104,990	$ (64,365)	$ (187,524)	$ (118,640)	$ (216,240)	$ 43,445	$ 9,303	$ 40,494	$ (265,539)		$ (122,998)		$ 165,274
Net income (loss) available (related) per share to common stockholders - Basic (in dollars per share)	$ 1.78	$ (1.09)	$ (3.14)	$ (2.21)	$ (5.07)	$ 1.03	$ 0.22	$ 0.97	$ (4.59)		$ (2.92)		$ 4.22
Net income (loss) available (related) per share to common stockholders - Diluted (in dollars per share)	1.78	(1.09)	(3.14)	(2.21)	(5.07)	1.02	0.22	0.96	(4.59)		(2.92)		4.17
Dividends declared per common share (in dollars per share)	$ 0.51	$ 0.51	$ 0.57	$ 0.57	$ 0.57	$ 0.57	$ 0.57	$ 0.57	$ 2.16		$ 2.28		$ 2.28
Weighted average common shares outstanding – basic (in shares)	58,902	59,077	59,654	53,630	42,656	42,047	41,912	41,887	57,833		42,128		39,170
Weighted average common shares outstanding - diluted (in shares)	59,149	59,077	59,654	53,630	42,656	42,435	42,328	42,331	57,833		42,128		39,642
Credit Risk and Non-Agency Securities
Condensed Income Statements, Captions [Line Items]
Debt securities, trading	$ 12,785	$ 13,158	$ 13,383	$ 13,592	$ 13,518	$ 14,573	$ 14,330	$ 14,006	$ 52,919		$ 56,427		$ 55,969
Debt securities, trading	1,650	(8,842)	(17,699)	496	(23,200)	(2,115)	(3,234)	1,283	(24,396)		(27,266)		65,672
Interest-Only Securities
Condensed Income Statements, Captions [Line Items]
Debt securities, trading	0	0	251	345	395	413	417	442	596		1,667		2,163
Debt securities, trading	0	0	490	(368)	(1,065)	210	(450)	298	123		(1,007)		(2,966)
U.S. Treasury Securities
Condensed Income Statements, Captions [Line Items]
Debt securities, trading	0	128	744	482	$ 591	$ 404	$ 2,805	$ 844	1,353		4,644		0
Debt securities, trading	0	(736)	3,453	(693)					2,024		(6,365)		0
Corporate Debt Securities
Condensed Income Statements, Captions [Line Items]
Debt securities, trading	$ 324	$ 479	$ 544	$ 539					$ 1,886		$ 2,019		$ 0

[1] Interest expense related to our interest rate swap contracts is recorded as realized loss on derivatives on the consolidated statements of operations. For additional information, see Note 8 to the consolidated financial statements.