Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 90,981	$ 63,807	$ 235,952	$ 167,062
Available for sale securities:
Unrealized (losses) gains arising during the period	(29,262)	4,118	(75,479)	22,581
Income tax benefit (expense) related to unrealized (losses) gains	7,471	(1,594)	19,270	(8,745)
Reclassification adjustment for net realized losses (gains) in earnings	0	6	(14)	(27)
Income tax (benefit) expense related to net realized losses (gains)	0	(3)	4	10
Net change in unrealized (losses) gains for available for sale securities	(21,791)	2,527	(56,219)	13,819
Junior subordinated debentures, at fair value:
Unrealized losses arising during the period	(2,409)	0	(5,605)	0
Income tax benefit related to unrealized losses	615	0	1,431	0
Net change in unrealized losses for junior subordinated debentures, at fair value	(1,794)	0	(4,174)	0
Other comprehensive (loss) income, net of tax	(23,585)	2,527	(60,393)	13,819
Comprehensive income	$ 67,396	$ 66,334	$ 175,559	$ 180,881