Consolidated Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 35,992	$ 26,977
Change in securities available-for-sale:
Unrealized holding gains (losses) for the period	15,780	17,857
Reclassification adjustment for securities gains realized in income	(1,500)	(1,106)
Income tax effect	(5,260)	(6,168)
Unrealized gains (losses) on available-for-sale securities	9,020	10,583
Change in securities held-to-maturity:
Amortization of fair value for securities held-to-maturity previously recognized into accumulated other comprehensive income	449	465
Income tax effect	(154)	(159)
Changes from securities held-to-maturity	295	306
Cash flow hedges:
Net unrealized derivative gains (losses) on cash flow hedges	580	(11,130)
Reclassification adjustment for losses realized in net income	1,799	1,273
Income tax effect	(904)	3,746
Changes from cash flow hedges	1,475	(6,111)
Defined benefit pension plans:
Amortization of net loss recognized in income	27	700
Income tax effect	(10)	(266)
Changes from defined benefit pension plans	17	434
Other comprehensive income (loss), net of tax	10,807	5,212
Comprehensive income	$ 46,799	$ 32,189