Accumulated Other Comprehensive Loss - Reclassifications from AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	$ (18,961)	$ (20,714)	$ (32,145)	$ (38,785)
Total net of tax	72,802	50,065	114,767	96,160
Interest expense	(69,366)	(42,187)	(129,263)	(78,774)
Total reclassifications, net of tax	(773)	(1,363)	(2,453)	(2,823)
Unrealized (losses) gains on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(30)		(578)
Non-credit impairment losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(12)		4
Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(619)		(1,655)
Defined benefit pension plan
Reclassification Out Of Accumulated Other Comprehensive Loss
Amortization of net loss	(157)	(101)	(314)	(202)
Tax effect	45	42	90	84
Total reclassifications, net of tax	(112)	(59)	(224)	(118)
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(866)	(2,314)	(2,317)	(4,832)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized (losses) gains on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
(Losses) gains on securities transactions, net	(36)	22	(801)	(1)
Tax effect	6	(9)	223	1
Total net of tax	(30)	13	(578)	0
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Non-credit impairment losses on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	4	(28)	(2)	(89)
Total net of tax	(12)	39	4	126
Interest and dividends on investment securities (taxable)	(16)	67	6	215
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	247	958	662	2,001
Total net of tax	(619)	(1,356)	(1,655)	(2,831)
Interest expense	$ (866)	$ (2,314)	$ (2,317)	$ (4,832)