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	$ 22,979	$ 26,132
Securities available for sale:
Unrealized gains arising during the period, net of tax expense of $3,248 and $7,719	6,032	14,335
Reclassification adjustment for gains included in net income, net of tax expense of $424 and $25	(787)	(46)
Derivative instruments:
Unrealized (losses) gains arising during the period, net of tax (benefit) expense of $(550) and $1,693	(1,022)	3,145
Reclassification adjustment for gains included in net income, net of tax expense of $125 and $188	(233)	(349)
Pension and postretirement benefit obligations:
Unrealized gains arising during the period, net of tax expense of $221 and $214	410	397
Other comprehensive income	4,400	17,482
Comprehensive income	$ 27,379	$ 43,614