Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 90,930	$ 68,014	$ 59,582
Securities available for sale:
Unrealized holding (losses) gains on securities	(6,206)	(351)	7,731
Reclassification adjustment for gains realized in net income	(727)	(59)	(232)
Amortization of unrealized holding gains on securities transferred to the held to maturity category	(61)	(110)	(156)
Total securities available for sale	(6,994)	(520)	7,343
Derivative instruments:
Unrealized holding gains (losses) on derivative instruments	527	(249)	(1,622)
Total derivative instruments	527	(249)	(1,622)
Defined benefit pension and post-retirement benefit plans:
Net gain (loss) arising during the period	31	(1,435)	(1,529)
Less amortization of net actuarial loss recognized in net periodic pension cost	302	267	183
Less amortization of net actuarial loss recognized in net periodic pension cost	(235)	0	0
Total defined benefit pension and post-retirement benefit plans	98	(1,168)	(1,346)
Other comprehensive (loss) income, net of tax	(6,369)	(1,937)	4,375
Comprehensive income	$ 84,561	$ 66,077	$ 63,957