Stockholders' Equity - Summary of Items in Consolidated Income Statements Affected by Amounts Reclassified from Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ (38,119)	$ (41,479)	$ (51,682)
Tax effect	66,465	52,510	45,613
Amount reclassified from accumulated other comprehensive income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	2,396	1,402
Amount reclassified from accumulated other comprehensive income [Member] | Gains and losses on sale of AFS securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Gains and losses on sale of AFS securities		(105)
Tax effect		(37)
Net of tax		(68)
Amount reclassified from accumulated other comprehensive income [Member] | Unrealized Gains And Losses On Securities Available For Sale Transferred To Held To Maturity [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization/accretion of unrealized net gain/loss on securities transferred to HTM	3,297	(6,371)
Tax effect	1,154	(2,230)
Net of tax	2,143	(4,141)
Amount reclassified from accumulated other comprehensive income [Member] | Amortization of defined benefit pension and post-retirement items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of defined benefit pension and post-retirement items	390	8,331
Tax effect	137	2,916
Net of tax	253	5,415
Amount reclassified from accumulated other comprehensive income [Member] | Gains and losses on cash flow hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense		301
Tax effect		105
Net of tax		$ 196