Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net Income	$ 98,387	$ 92,349	$ 82,064
Unrealized holding gains (losses):
Before tax	12,641	(19,204)	(9,824)
Tax effect	(5,077)	7,682	3,906
Net of tax	7,564	(11,522)	(5,918)
Reclassification of net (losses) gains included in net income:
Before tax	(1,876)	1,420	2,373
Tax effect	771	(568)	(970)
Net of tax	(1,105)	852	1,403
Net unrealized holding gains (losses)	8,669	(12,374)	(7,321)
Derivative Instruments
Before tax	(4,333)	2,175	(2,233)
Tax effect	1,746	(883)	903
Net of tax	(2,587)	1,292	(1,330)
Net unrealized holding gains (losses)
Before tax	2,988	(2,002)	(6,570)
Tax effect	(1,196)	563	2,687
Net of tax	1,792	(1,439)	(3,883)
Total other comprehensive income (loss)	7,874	(12,521)	(12,534)
Total comprehensive income	$ 106,261	$ 79,828	$ 69,530