Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 38,854	$ 39,122	$ 74,846	$ 66,099
Change in securities available-for-sale:
Unrealized holding gains (losses) for the period	30,627	12,671	46,407	30,528
Reclassification adjustment for securities gains realized in income	(3,075)	(1,856)	(4,575)	(2,962)
Income tax effect	(10,017)	(3,809)	(15,277)	(9,977)
Unrealized gains (losses) on available-for-sale securities	17,535	7,006	26,555	17,589
Change in securities held-to-maturity:
Amortization of fair value for securities held-to-maturity previously recognized into accumulated other comprehensive income	453	466	902	931
Income tax effect	(155)	(159)	(309)	(318)
Changes from securities held-to-maturity	298	307	593	613
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	(2,387)	(4,483)	(1,807)	(15,613)
Reclassification adjustment for losses realized in net income	1,734	1,585	3,533	2,858
Income tax effect	248	1,101	(656)	4,847
Changes from cash flow hedges	(405)	(1,797)	1,070	(7,908)
Defined benefit pension plans:
Amortization of net loss recognized in income	27	730	54	1,430
Income tax effect	(10)	(278)	(20)	(544)
Changes from defined benefit pension plans	17	452	34	886
Other comprehensive income (loss), net of tax	17,445	5,968	28,252	11,180
Comprehensive income	$ 56,299	$ 45,090	$ 103,098	$ 77,279