Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 100,763	$ 77,693	$ 272,731	$ 175,078
Securities available for sale:
Unrealized (losses) gains arising during the period, net of tax (benefit) expense of $(3,502), $724, $(14,492) and $4,503	(12,310)	1,288	(50,970)	8,027
Reclassification adjustment for gains included in net income, net of tax expense of $0, $215, $7 and $223	0	(384)	(24)	(398)
Derivative instruments:
Unrealized gains (losses) arising during the period, net of tax expense (benefit) of $396, $76, $1,989 and $(1,265)	1,391	136	6,991	(2,254)
Reclassification adjustment for (gains) losses included in net income, net of tax expense (benefit) of $141, $(44), $346 and $45	(495)	78	(1,216)	(81)
Pension and postretirement benefit obligations:
Unrealized gains arising during the period, net of tax expense of $130, $535, $404 and $987	459	955	1,431	1,765
Other Comprehensive (Loss) Income	(10,955)	2,073	(43,788)	7,059
Comprehensive Income	$ 89,808	$ 79,766	$ 228,943	$ 182,137