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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Equity [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Before Tax Amount	$ (551)	$ 40,122	$ (95,920)	$ 62,972
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Before Tax Amount	(8,054)	0	(26,258)	0
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Before Tax Amount	14	0	3	121
Total securities available for sale and transferred securities, Before Tax Amount	(8,591)	40,122	(122,175)	63,093
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Before Tax Amount	1,640	1,427	4,919	4,084
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Before Tax Amount	(15)	(269)	(48)	(760)
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	1,120	1,063	3,308	3,140
Total derivatives, Before Tax Amount	(8,240)	(8,551)	(24,775)	(25,655)
Total other comprehensive income, Before Tax Amount	(15,191)	32,998	(142,031)	41,522
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Tax Expense (Benefit)	(193)	14,043	(33,572)	22,041
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Tax Expense (Benefit)	(2,818)	0	(9,190)	0
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Tax Expense (Benefit)	5	0	1	42
Total securities available for sale and transferred securities, Tax Expense (Benefit)	(3,006)	14,043	(42,761)	22,083
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Tax Expense (Benefit)	574	499	1,722	1,429
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Tax Expense (Benefit)	(5)	(93)	(17)	(266)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Tax Expense (Benefit)	(3,271)	(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)	392	372	1,158	1,099
Total derivatives, Tax Expense (Benefit)	(2,884)	(2,992)	(8,671)	(8,979)
Total other comprehensive income, Tax Expense (Benefit)	(5,316)	11,550	(49,710)	14,533
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Net of Tax	(358)	26,079	(62,348)	40,931
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Net of Tax	(5,236)	0	(17,068)	0
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Net of Tax	9	0	2	79
Total securities available for sale and transferred securities, Net of Tax	(5,585)	26,079	(79,414)	41,010
Defined-benefit post-retirement benefit plans,Change in the net actuarial gain/loss, Net of Tax	1,066	928	3,197	2,655
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Net of Tax	(10)	(176)	(31)	(494)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Net of Tax	(6,074)	(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	728	691	2,150	2,041
Total derivatives, Net of Tax	(5,356)	(5,559)	(16,104)	(16,676)
Other comprehensive income (loss), net of tax	$ (9,875)	$ 21,448	$ (92,321)	$ 26,989