Accumulated Other Comprehensive Loss - Reclassifications (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest and dividends on investment securities (taxable)	$ 67	$ 0	$ 216	$ 489
Interest expense	(42,187)	(37,573)	(78,774)	(75,017)
Tax effect	(20,714)	(15,460)	(38,785)	(29,849)
Total net of tax	50,065	39,027	96,160	75,214
Total reclassifications, net of tax	(1,363)	(2,152)	(2,823)	(3,480)
Unrealized gains (losses) on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	13		0
Non-credit impairment losses on AFS securities before tax:
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	39		126
Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(1,356)		(2,831)
Defined benefit pension plan:
Reclassification Out Of Accumulated Other Comprehensive Loss
Amortization of net loss	(101)	(72)	(202)	(144)
Tax effect	42	29	84	58
Total reclassifications, net of tax	(59)	(43)	(118)	(86)
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(2,314)	(3,597)	(4,832)	(6,568)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized gains (losses) on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains (losses) on securities transactions, net	22	(3)	(1)	268
Tax effect	(9)	1	1	(100)
Total net of tax	13	(2)	0	168
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Non-credit impairment losses on AFS securities before tax:
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest and dividends on investment securities (taxable)	67	0	215	489
Tax effect	(28)	0	(89)	(203)
Total net of tax	39	0	126	286
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(2,314)	(3,597)	(4,832)	(6,568)
Tax effect	958	1,490	2,001	2,720
Total net of tax	$ (1,356)	$ (2,107)	$ (2,831)	$ (3,848)