Stockholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			$ (35,379)	$ (22,925)
Net change in unrealized (losses) gains	(6,293)	(9,685)	9,119	(96,074)
Reclassification of net losses realized and included in earnings			2,195	5,835
Amortization of unrealized net gain (loss) on securities transferred to held to maturity	892	(1,456)	2,463	(7,099)
Income tax (benefit) expense			5,091	(35,492)
Accumulated other comprehensive income (loss), Ending balance	(26,693)	(84,771)	(26,693)	(84,771)
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 (losses) gains			9,119	(96,070)
Transfer of net unrealized gain from AFS to HTM, net of cumulative tax effect				36,208
Income tax (benefit) expense			3,309	(35,115)
Accumulated other comprehensive income (loss), Ending balance	14,073	14,107	14,073	14,107
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
Transfer of net unrealized gain from AFS to HTM, net of cumulative tax effect				(36,208)
Amortization of unrealized net gain (loss) on securities transferred to held to maturity			2,463	(7,099)
Income tax (benefit) expense			879	(2,563)
Accumulated other comprehensive income (loss), Ending balance	(19,605)	(21,654)	(19,605)	(21,654)
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			(22,453)	(80,688)
Reclassification of net losses realized and included in earnings			2,195	5,534
Income tax (benefit) expense			903	2,070
Accumulated other comprehensive income (loss), Ending balance	(21,161)	(77,224)	(21,161)	(77,224)
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 (losses) gains				(4)
Reclassification of net losses realized and included in earnings				301
Income tax (benefit) expense				$ 116