Other Comprehensive Income (Loss) - Component of 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
Equity [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Before Tax Amount	$ 9,464	$ (551)	$ 76,007	$ (95,920)
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Before Tax Amount	(8,746)	(8,054)	(27,119)	(26,258)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Before Tax Amount	(33)	14	(35)	3
Total securities available for sale and transferred securities, Before Tax Amount	685	(8,591)	48,853	(122,175)
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Before Tax Amount	672	1,640	2,015	4,919
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Before Tax Amount	0	(15)	0	(48)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Before Tax Amount	(9,345)	(9,345)	(28,035)	(28,035)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Before Tax Amount	0	1,120	0	3,308
Total derivatives, Before Tax Amount	(9,345)	(8,240)	(28,035)	(24,775)
Total other comprehensive income (loss), before tax	(7,988)	(15,191)	22,833	(142,031)
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Tax Expense (Benefit)	3,312	(193)	26,602	(33,572)
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Tax Expense (Benefit)	(3,061)	(2,818)	(9,492)	(9,190)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Tax Expense (Benefit)	(12)	5	(12)	1
Total securities available for sale and transferred securities, Tax Expense (Benefit)	239	(3,006)	17,098	(42,761)
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Tax Expense (Benefit)	235	574	705	1,722
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Tax Expense (Benefit)	0	(5)	0	(17)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Tax Expense (Benefit)	(3,270)	(3,271)	(9,812)	(9,812)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Tax Expense (Benefit)	0	392	0	1,158
Total derivatives, Tax Expense (Benefit)	(3,270)	(2,884)	(9,812)	(8,671)
Total other comprehensive income (loss), Tax Expense (Benefit)	(2,796)	(5,316)	7,991	(49,710)
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Net of Tax	6,152	(358)	49,405	(62,348)
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Net of Tax	(5,685)	(5,236)	(17,627)	(17,068)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Net of Tax	(21)	9	(23)	2
Total securities available for sale and transferred securities, Net of Tax	446	(5,585)	31,755	(79,414)
Defined-benefit post-retirement benefit plans,Change in the net actuarial gain/loss, Net of Tax	437	1,066	1,310	3,197
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Net of Tax	0	(10)	0	(31)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Net of Tax	(6,075)	(6,074)	(18,223)	(18,223)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Net of Tax	0	728	0	2,150
Total derivatives, Net of Tax	(6,075)	(5,356)	(18,223)	(16,104)
Other comprehensive income (loss), net of tax	$ (5,192)	$ (9,875)	$ 14,842	$ (92,321)