Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 54,545	$ 53,352	$ 147,617	$ 116,462
Unrealized holding gains (losses):
Before tax	13,636	(13,632)	78,625	(47,765)
Tax effect	(3,800)	3,548	(21,900)	13,055
Net of tax	9,836	(10,084)	56,725	(34,710)
Derivative Instruments
Before tax	(399)		3,500
Before tax		(880)		(948)
Tax effect	111		(975)
Tax effect		231		250
Net of tax	(288)		2,525
Net of tax		(649)		(698)
Total other comprehensive income (loss)	9,548	(10,733)	59,250	(35,408)
Total comprehensive income	$ 64,093	$ 42,619	$ 206,867	$ 81,054