Consolidated Statements of Comprehensive Income - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 134,264,000	$ 116,716,000	$ 103,667,000
Change in securities available-for-sale:
Unrealized holding gains (losses) for the period	(49,813,000)	1,173,000	42,515,000
Reclassification adjustment for securities gains realized in income	(5,848,000)	(5,718,000)	(9,830,000)
Other-than-temporary-impairment on available-for-sale securities associated with credit loss realized in income	0	0	100,000
Income tax effect	20,455,000	1,487,000	(12,425,000)
Unrealized gains (losses) on available-for-sale securities	(35,206,000)	(3,058,000)	20,360,000
Change in securities held-to-maturity:
Amortization of fair value for securities held-to-maturity previously recognized into accumulated other comprehensive income	1,776,000	1,692,000	1,437,000
Income tax effect	(606,000)	(396,000)	(446,000)
Changes from securities held-to-maturity	1,170,000	1,296,000	991,000
Cash flow hedges:
Net unrealized derivative losses on cash flow hedges	(2,323,000)	(8,107,000)	(9,514,000)
Reclassification adjustment for losses realized in net income	6,453,000	2,719,000	248,000
Income tax effect	(1,569,000)	2,047,000	3,521,000
Changes from cash flow hedges	2,561,000	(3,341,000)	(5,745,000)
Defined benefit pension plans:
Amortization of net (gain) loss and settlement cost recognized in income	11,203,000	3,002,000	(4,333,000)
Income tax effect	(4,303,000)	(1,141,000)	1,638,000
Changes from defined benefit pension plans	6,900,000	1,861,000	(2,695,000)
Other comprehensive income (loss), net of tax	(24,575,000)	(3,242,000)	12,911,000
Comprehensive income	$ 109,689,000	$ 113,474,000	$ 116,578,000