Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 170,891	$ 159,649	$ 144,050
Securities available for sale:
Unrealized (losses) gains arising during the period, net of tax (benefit) expense of $(7,477), $(1,561), and $13,593	(13,886)	(2,899)	25,242
Reclassification adjustment for gains included in net income, net of tax expense of $249, $288 and $4,101	(463)	(534)	(7,616)
Derivative instruments:
Unrealized gains arising during the period, net of tax expense of $2,739, $1,887 and $4,629	5,086	3,504	8,597
Reclassification adjustment for gains included in net income, net of tax expense of $685, $1,035 and $1,160	(1,272)	(1,921)	(2,154)
Pension and postretirement benefit obligations:
Unrealized gains (losses) arising during the period, net of tax expense (benefit) of $161, $(1,766) and $(7,080)	299	(3,280)	(13,148)
Other comprehensive (loss) income	(10,236)	(5,130)	10,921
Comprehensive income	$ 160,655	$ 154,519	$ 154,971