Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 23,179	$ 16,220	$ 67,295	$ 46,854
Securities available for sale:
Unrealized holding gains on securities	1,385	3,717	5,260	2,505
Reclassification adjustment for gains realized in net income	0	0	(728)	(60)
Amortization of unrealized holding gains on securities transferred to the held to maturity category	(11)	(26)	(49)	(86)
Total securities	1,374	3,691	4,483	2,359
Derivative instruments:
Unrealized holding gains (losses) on derivative instruments	495	(1,075)	(1,199)	(881)
Totals derivative instruments	495	(1,075)	(1,199)	(881)
Defined benefit pension and post-retirement benefit plans:
Reclassification adjustment for net settlement gain realized in net income	(235)	0	(235)	0
Amortization of net actuarial loss recognized in net periodic pension cost	76	55	228	180
Total defined benefit pension and post-retirement benefit plans	(159)	55	(7)	180
Other comprehensive income, net of tax	1,710	2,671	3,277	1,658
Comprehensive income	$ 24,889	$ 18,891	$ 70,572	$ 48,512