Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income, Note 1	$ 65,999	$ 57,219	$ 144,971	$ 103,255
Available for sale securities:
Unrealized (losses) gains arising during the period	(4,027)	14,321	(46,217)	18,463
Income tax benefit (expense) related to unrealized (losses) gains	1,028	(5,547)	11,799	(7,151)
Reclassification adjustment for net realized gains in earnings	(14)	(35)	(14)	(33)
Income tax expense related to realized gains	4	14	4	13
Net change in unrealized (losses) gains for available for sale securities	(3,009)	8,753	(34,428)	11,292
Junior subordinated debentures, at fair value:
Unrealized losses arising during the period	(1,513)	0	(3,196)	0
Income tax benefit related to unrealized losses	386	0	816	0
Net change in unrealized losses for junior subordinated debentures, at fair value	(1,127)	0	(2,380)	0
Other comprehensive (loss) income, net of tax	(4,136)	8,753	(36,808)	11,292
Comprehensive income	$ 61,863	$ 65,972	$ 108,163	$ 114,547