Stockholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			$ (22,925)	$ (26,510)
Other comprehensive income before income taxes:
Net change in unrealized gain (loss)	(9,685)	10,821	(96,074)	24,410
Reclassification of net (gains) losses realized and included in earnings			5,835	4,371
Amortization/accretion of unrealized net gain/loss on securities transferred to HTM	(1,456)	(2,725)	(7,099)	(5,645)
Income tax expense (benefit)			(35,492)	8,413
Accumulated other comprehensive income (loss), Ending balance	(84,771)	(11,787)	(84,771)	(11,787)
Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			38,854	60,478
Other comprehensive income before income taxes:
Net change in unrealized gain (loss)			(96,070)	24,780
Transfer of net unrealized gain from AFS to HTM, net of cumulative tax effect			36,208	(24,598)
Reclassification of net (gains) losses realized and included in earnings				(929)
Income tax expense (benefit)			(35,115)	8,693
Accumulated other comprehensive income (loss), Ending balance	14,107	51,038	14,107	51,038
HTM Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			19,090
Other comprehensive income before income taxes:
Transfer of net unrealized gain from AFS to HTM, net of cumulative tax effect			(36,208)	24,598
Amortization/accretion of unrealized net gain/loss on securities transferred to HTM			(7,099)	(5,645)
Income tax expense (benefit)			(2,563)	(2,122)
Accumulated other comprehensive income (loss), Ending balance	(21,654)	21,075	(21,654)	21,075
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			(80,688)	(86,923)
Other comprehensive income before income taxes:
Reclassification of net (gains) losses realized and included in earnings			5,534	5,260
Income tax expense (benefit)			2,070	1,971
Accumulated other comprehensive income (loss), Ending balance	(77,224)	(83,634)	(77,224)	(83,634)
Loss on Effective Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance			(181)	(65)
Other comprehensive income before income taxes:
Net change in unrealized gain (loss)			(4)	(370)
Reclassification of net (gains) losses realized and included in earnings			301	40
Income tax expense (benefit)			116	(129)
Accumulated other comprehensive income (loss), Ending balance		$ (266)		$ (266)