Accumulated Other Comprehensive Income (Loss) - Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains	$ 1,856	$ 512	$ 2,962	$ 3,195
Interest income/(expense)	99,340	92,097	184,983	183,090
Salaries and employee benefits, Actuarial gains/(losses)	730	725	1,430	1,463
Income tax (expense) benefit	(30,812)	(8,959)	(40,483)	(18,184)
Net income	39,122	26,156	66,099	47,062
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(540)	(679)	(1,370)	34
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains	1,856	512	2,962	3,195
Income tax (expense) benefit	(654)	(186)	(1,061)	(1,181)
Net income	1,202	326	1,901	2,014
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Unrealized Gains and Losses on Held-to-Maturity Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income/(expense)	(466)	(430)	(931)	(767)
Income tax (expense) benefit	159	147	318	81
Net income	(307)	(283)	(613)	(686)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Gains and Losses on Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax (expense) benefit	602	167	1,086	238
Net income	(983)	(272)	(1,772)	(387)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Gains and Losses on Cash Flow Hedges [Member] | Interest Rate Contracts [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income/(expense)	(1,585)	(439)	(2,858)	(625)
Reclassifications out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Defined Benefit Pension Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Salaries and employee benefits, Actuarial gains/(losses)	(730)	(725)	(1,430)	(1,463)
Income tax (expense) benefit	278	275	544	556
Net income	$ (452)	$ (450)	$ (886)	$ (907)