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	$ 23,972	$ 21,216
Securities available for sale:
Unrealized holding gains on securities	2,907	3,107
Amortization of unrealized holding gains on securities transferred to the held to maturity category	(151)	(20)
Total securities	2,756	3,087
Derivative instruments:
Unrealized holding gains (losses) on derivative instruments	169	(1,266)
Total derivative instruments	169	(1,266)
Defined benefit pension and post-retirement benefit plans:
Amortization of net actuarial loss recognized in net periodic pension cost	69	72
Total defined benefit pension and post-retirement benefit plans	69	72
Other comprehensive income, net of tax	2,994	1,893
Comprehensive income	$ 26,966	$ 23,109