Summarized Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Net interest income:
Interest income	$ 301,957	$ 296,813	$ 288,644	$ 251,344	$ 260,823	$ 250,953	$ 221,096	$ 201,194	$ 1,138,758	[1]	$ 934,068	[1]	$ 872,737	[1]
Interest expense	144,204	140,358	137,955	110,231	106,737	94,911	83,227	62,981	532,748	[2]	347,857	[2]	259,365	[2]
Net interest income	157,753	156,455	150,689	141,113	154,086	156,042	137,869	138,213	606,010		586,211		613,372
Other-than-temporary impairments:
Total other-than-temporary impairment losses	(923)	(784)	(749)	(2,713)	(1,034)	(993)	(3,129)	(4,423)
Portion of loss recognized in other comprehensive income (loss)	(17,256)	(10,684)	(12,760)	(15,988)	(13,746)	(10,581)	(17,816)	(6,255)
Net other-than-temporary credit impairment losses	(18,179)	(11,468)	(13,509)	(18,701)	(14,780)	(11,574)	(20,955)	(10,678)	(61,856)		(57,987)		(67,444)
Net gains (losses) on derivatives	31,108	1,363	(21,822)	(4,462)	115,523	13,360	(47,755)	(136,537)	6,188		(55,409)		(114,637)
Net unrealized gains (losses) on financial instruments at fair value	(47,637)	19,042	67,762	72,243	(20,664)	32,999	30,347	16,871	111,410		59,552		(158,433)
Net realized gains (losses) on sales of investments	(586)	1	4,541	5,167	11,121	3,079	6,631	(2,674)	9,123		18,155		77,074
Gain (loss) on Extinguishment of Debt	12,742	(1)	(48,014)	0	1,334	(45)	0	(1,766)	(35,274)		(477)		(5,930)
Other income					0	0	0	95,000	0		95,000		0
Total other expenses	27,657	26,142	24,491	32,537	24,698	21,031	31,987	15,302	110,825		93,019		93,396
Net income (loss)	107,608	139,232	115,017	162,807	221,903	172,817	74,127	83,098	524,668		551,943		250,349
Dividend on preferred stock	9,400	9,400	9,400	5,283	2,449	0	0	0	33,484		2,449		0
Net income (loss) available to common shareholders	$ 98,208	$ 129,832	$ 105,617	$ 157,524	$ 219,454	$ 172,817	$ 74,127	$ 83,098	$ 491,184		$ 549,494		$ 250,349
Net income per common share-basic (usd per share)	$ 0.52	$ 0.69	$ 0.56	$ 0.84	$ 1.17	$ 0.92	$ 0.39	$ 0.44	$ 2.62		$ 2.93		$ 1.25

[1] Includes interest income of consolidated VIEs of $914,022, $678,623 and $575,715 for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 8 to consolidated financial statements for further discussion.

[2] Includes interest expense of consolidated VIEs of $390,858, $249,708 and $191,922 for the years ended December 31, 2017, 2016 and 2015, respectively. See Note 8 to consolidated financial statements for further discussion.