Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended																								3 Months Ended								12 Months Ended
	Dec. 31, 2019	[1]	Nov. 30, 2019	[1]	Oct. 31, 2019	[1]	Sep. 30, 2019	[1]	Aug. 31, 2019	[1]	Jul. 31, 2019	[1]	Jun. 30, 2019	[1]	May 31, 2019	[1]	Apr. 30, 2019	[1]	Mar. 31, 2019	[1]	Feb. 28, 2019	[1]	Jan. 31, 2019	[1]	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
Quarterly Financial Information [Abstract]
Interest income																									$ 41,961	$ 44,502	$ 43,748	$ 39,957	$ 32,014	$ 26,925	$ 25,922	$ 25,190	$ 170,168	$ 110,051	$ 94,502
Interest expense																									25,766	31,256	30,813	26,276	19,053	14,751	14,175	11,595	114,111	59,574	36,178
Interest Income (Expense), Net																									16,195	13,246	12,935	13,681	12,961	12,174	11,747	13,595	56,057	50,477	58,324
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net																									42,992	(50,709)	(117,535)	(61,697)	(81,981)	19,499	20,667	38,354	(186,949)	(3,461)	3,044
Loss on sale of investments, net																									0	4,605	(10,360)	0	(5,428)	(1,726)	(12,444)	(3,775)	(5,755)	(23,373)	(11,530)
Fair value adjustments, net																									(14)	(13)	(16)	(13)	(16)	12	27	29	(56)	52	75
Other operating income (expense), net																									(28)	25	256	(231)	(566)	(409)	(339)	(253)	22	(1,567)	(201)
General and Administrative Expense																									(4,010)	(3,758)	(4,265)	(3,954)	(3,492)	(3,964)	(4,006)	(3,643)
Preferred stock dividends																									(3,361)	(3,341)	(3,206)	(3,059)	(2,963)	(2,956)	(2,942)	(2,940)	(12,967)	(11,801)	(10,794)
Net (loss) income to common stockholders																									51,774	(39,945)	(122,191)	(55,273)	(81,485)	22,630	12,710	41,367	(165,635)	(4,778)	23,099
Other Comprehensive Income (Loss), Net of Tax																									(43,204)	55,195	111,127	86,467	50,054	(21,914)	(9,760)	(45,462)	209,585	(27,082)	23,912
Comprehensive income (loss) to common shareholders																									$ 8,570	$ 15,250	$ (11,064)	$ 31,194	$ (31,431)	$ 716	$ 2,950	$ (4,095)	$ 43,950	$ (31,860)	$ 47,011
Net (loss) income per common share-basic and diluted																									$ 2.26	$ (1.65)	$ (4.98)	$ (2.42)	$ (4.02)	$ 1.18	$ 0.68	$ 2.22	$ (7.01)	$ (0.25)	$ 1.37
Common Stock, Dividends, Per Share, Declared	$ 0.15		$ 0.15		$ 0.15		$ 0.15		$ 0.15		$ 0.18		$ 0.18		$ 0.18		$ 0.18		$ 0.18		$ 0.18		$ 0.18		$ 0.45	$ 0.48	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54	$ 0.54

[1] Amounts declared have been adjusted to reflect the effect of the 1-for-3 reverse stock split.