Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 21,216	$ 15,240
Securities available for sale:
Unrealized holding gains on securities	3,107	2,624
Amortization of unrealized holding gains on securities transferred to the held to maturity category	(20)	(32)
Total securities	3,087	2,592
Derivative instruments:
Unrealized holding losses on derivative instruments	(1,266)	(669)
Totals derivative instruments	(1,266)	(669)
Defined benefit pension and post-retirement benefit plans:
Amortization of net actuarial gain recognized in net periodic pension cost	72	57
Total defined benefit pension and post-retirement benefit plans	72	57
Other comprehensive income, net of tax	1,893	1,980
Comprehensive income	$ 23,109	$ 17,220