Stockholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance	$ (22,925)	$ (26,510)	$ (619)
Other comprehensive income before income taxes:
Net change in unrealized gain (loss)	(22,621)	8,140	(42,655)
Reclassification adjustment for net losses realized and included in earnings	8,527	6,327	2,923
Amortization of unrealized net gain on securities transferred to held-to-maturity	(6,371)	(8,752)
Income tax expense (benefit)	(8,011)	2,130	(13,841)
Accumulated other comprehensive income (loss), Ending balance	(35,379)	(22,925)	(26,510)
Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance	38,854	60,478	27,232
Other comprehensive income before income taxes:
Net change in unrealized gain (loss)	(105,270)	6,076	52,300
Transfer of net unrealized gain from AFS to HTM, net of cummulative tax effect	36,208	(24,598)
Reclassification adjustment for net losses realized and included in earnings	(105)	(1,441)	91
Income tax expense (benefit)	(38,576)	1,661	19,145
Accumulated other comprehensive income (loss), Ending balance	8,263	38,854	60,478
Held to Maturity 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 cummulative tax effect	(36,208)	24,598
Amortization of unrealized net gain on securities transferred to held-to-maturity	(6,371)	(8,752)
Income tax expense (benefit)	(2,300)	(3,244)
Accumulated other comprehensive income (loss), Ending balance	(21,189)	19,090
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), Beginning balance	(80,688)	(86,923)	(27,851)
Other comprehensive income before income taxes:
Net change in unrealized gain (loss)	82,653	2,566	(94,848)
Reclassification adjustment for net losses realized and included in earnings	8,331	7,457	2,832
Income tax expense (benefit)	32,749	3,788	(32,944)
Accumulated other comprehensive income (loss), Ending balance	(22,453)	(80,688)	(86,923)
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)	(502)	(107)
Reclassification adjustment for net losses realized and included in earnings	301	311
Income tax expense (benefit)	116	(75)	(42)
Accumulated other comprehensive income (loss), Ending balance		$ (181)	$ (65)