Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 74,406	$ 41,300	$ 97,385	$ 67,432
Securities available for sale:
Unrealized gains arising during the period, net of tax expense of $403, $3,634, $3,779 and $11,353	720	6,750	6,739	21,085
Reclassification adjustment for (losses) gains included in net income, net of tax (benefit) expense of $(427), $79, $8 and $104	761	(147)	(14)	(193)
Derivative instruments:
Unrealized (losses) gains arising during the period, net of tax (benefit) expense of $(766), $834, $(1,341) and $2,527	(1,365)	1,548	(2,390)	4,693
Reclassification adjustment for (losses) gains included in net income, net of tax (benefit) expense of $(40), $191, $89 and $379	70	(355)	(159)	(704)
Pension and postretirement benefit obligations:
Unrealized gains arising during the period, net of tax expense of $224, $213, $452 and $427	400	396	810	793
Other comprehensive income	586	8,192	4,986	25,674
Comprehensive income	$ 74,992	$ 49,492	$ 102,371	$ 93,106