Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 33,826	$ 23,972
Securities available for sale:
Unrealized holding (losses) gains on securities	(7,909)	2,907
Amortization of unrealized holding gains on securities transferred to the held to maturity category	0	(151)
Total securities	(7,909)	2,756
Derivative instruments:
Unrealized holding gains on derivative instruments	858	169
Total derivative instruments	858	169
Defined benefit pension and post-retirement benefit plans:
Amortization of net actuarial loss recognized in net periodic pension cost	66	69
Total defined benefit pension and post-retirement benefit plans	66	69
Other comprehensive (loss) income, net of tax	(6,985)	2,994
Comprehensive income	$ 26,841	$ 26,966