Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 111,810	$ 65,999	$ 185,843	$ 144,971
Available for sale securities:
Unrealized gains (losses) arising during the period	40,760	(4,027)	74,029	(46,217)
Income tax (expense) benefit related to unrealized gains (losses)	(10,484)	1,028	(19,041)	11,799
Reclassification adjustment for net realized losses (gains) in earnings	7,186	(14)	7,186	(14)
Income tax (benefit) expense related to realized losses (gains)	(1,848)	4	(1,848)	4
Net change in unrealized gains (losses) for available for sale securities	35,614	(3,009)	60,326	(34,428)
Junior subordinated debentures, at fair value:
Unrealized gains (losses) arising during the period	17,240	(1,513)	23,804	(3,196)
Income tax (expense) benefit related to unrealized gains (losses)	(4,459)	386	(6,103)	816
Net change in unrealized gains (losses) for junior subordinated debentures, at fair value	12,781	(1,127)	17,701	(2,380)
Other comprehensive income (loss), net of tax	48,395	(4,136)	78,027	(36,808)
Comprehensive income	$ 160,205	$ 61,863	$ 263,870	$ 108,163