Stockholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			$ (35,379)	$ (22,925)
Net change in unrealized gain (loss)	10,898	(73,951)	15,412	(86,389)
Reclassification of net (gains) losses realized and included in earnings			2,201	4,282
Amortization of unrealized net gain on securities transferred to held to maturity	906	(2,659)	1,571	(5,643)
Income tax expense (benefit)			7,096	(31,980)
Accumulated other comprehensive income (loss), Ending balance	(23,291)	(78,695)	(23,291)	(78,695)
Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			8,263	38,854
Net change in unrealized gain (loss)			15,412	(86,385)
Reclassification of net (gains) losses realized and included in earnings
Amortization of unrealized net gain on securities transferred to held to maturity
Income tax expense (benefit)			5,637	(31,544)
Accumulated other comprehensive income (loss), Ending balance	18,038	(15,987)	18,038	(15,987)
Held to Maturity Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			(21,189)	19,090
Net change in unrealized gain (loss)
Reclassification of net (gains) losses realized and included in earnings
Amortization of unrealized net gain on securities transferred to held to maturity			1,571	(5,643)
Income tax expense (benefit)			554	(2,038)
Accumulated other comprehensive income (loss), Ending balance	(20,172)	15,485	(20,172)	15,485
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			(22,453)	(80,688)
Net change in unrealized gain (loss)
Reclassification of net (gains) losses realized and included in earnings			2,201	3,981
Amortization of unrealized net gain on securities transferred to held to maturity
Income tax expense (benefit)			905	1,486
Accumulated other comprehensive income (loss), Ending balance	(21,157)	(78,193)	(21,157)	(78,193)
Loss on Effective Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance				(181)
Net change in unrealized gain (loss)				(4)
Reclassification of net (gains) losses realized and included in earnings				301
Amortization of unrealized net gain on securities transferred to held to maturity
Income tax expense (benefit)				116
Accumulated other comprehensive income (loss), Ending balance