Summarized Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Net interest income:
Interest income	$ 340,662	$ 330,144	$ 339,914	$ 350,389	$ 348,033	$ 321,715	$ 306,436	$ 297,132	$ 1,361,110	[1]	$ 1,273,316	[1]	$ 1,138,758	[1]
Interest expense	169,203	188,551	198,110	202,950	193,920	174,671	161,266	149,251	758,814	[2]	679,108	[2]	532,748	[2]
Net interest income	171,459	141,593	141,804	147,439	154,113	147,044	145,170	147,881	602,296		594,208		606,010
Net other-than-temporary credit impairment losses	0	0	0	(4,853)	(4,269)	(7,233)	(9,131)	(1,158)	(4,853)		(21,791)		(61,856)
Net gains (losses) on derivatives	78,030	(136,671)	(237,079)	(204,638)	(315,877)	74,078	24,502	94,504	(500,358)		(122,793)		6,188
Net unrealized gains (losses) on financial instruments at fair value	(112,751)	130,825	190,748	200,812	84,836	(34,306)	(18,364)	14,466	409,634		46,632		111,410
Net realized gains (losses) on sales of investments	17,687	1,596	(7,526)	8,603	1,213	(6,123)	2,167	0	18,770		(2,844)		9,123
Gain (loss) on Extinguishment of Debt	9,926	0	(608)	0	7,055	9,263	387	9,670	9,318		26,376		(35,274)
Total other expenses	33,998	31,015	28,424	29,216	29,855	25,395	26,587	26,322	122,653		108,161		110,825
Net income (loss)	130,318	106,326	58,760	118,147	(102,798)	157,321	118,108	239,007	413,551		411,637		524,668
Dividends on preferred stock	18,438	18,438	18,438	17,392	14,437	9,960	9,400	9,400	72,704		43,197		33,484
Net income (loss) available to common shareholders	$ 111,880	$ 87,888	$ 40,322	$ 100,755	$ (117,235)	$ 147,361	$ 108,708	$ 229,607	$ 340,847		$ 368,440		$ 491,184
Net income per common share-basic (usd per share)	$ 0.60	$ 0.47	$ 0.22	$ 0.54	$ (0.63)	$ 0.79	$ 0.58	$ 1.22	$ 1.82		$ 1.97		$ 2.62

[1] Includes interest income of consolidated VIEs of $780,746, $904,830 and $914,022 for the years ended December 31, 2019, 2018 and 2017, respectively. See Note 8 to consolidated financial statements for further discussion.

[2] Includes interest expense of consolidated VIEs of $337,387, $395,255 and $390,858 for the years ended December 31, 2019, 2018 and 2017, respectively. See Note 8 to consolidated financial statements for further discussion.