Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 26,421	$ 23,179	$ 75,677	$ 67,295
Securities available for sale:
Unrealized holding gains on securities	(764)	1,385	4,712	5,260
Reclassification adjustment for gains realized in net income	0	0	0	(728)
Unrealized holding gains on securities transfered from held to maturity to available for sale	8,108	0	8,108	0
Amortization of unrealized holding gains on securities transferred to the held to maturity category	(4)	(11)	(173)	(49)
Total securities	7,340	1,374	12,647	4,483
Derivative instruments:
Unrealized holding gains (losses) on derivative instruments	100	495	104	(1,199)
Total derivative instruments	100	495	104	(1,199)
Defined benefit pension and post-retirement benefit plans:
Reclassification adjustment for net settlement gain realized in net income	0	(235)	0	(235)
Amortization of net actuarial loss recognized in net periodic pension cost	62	76	187	228
Total defined benefit pension and post-retirement benefit plans	62	(159)	187	(7)
Other comprehensive income, net of tax	7,502	1,710	12,938	3,277
Comprehensive income	$ 33,923	$ 24,889	$ 88,615	$ 70,572