Other Comprehensive Income (Loss) - Component of Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Earnings [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Before Tax Amount	$ (74,025)	$ 20,968	$ (95,369)	$ 22,850
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Before Tax Amount	(9,745)		(18,204)
Securities available for sale and transferred securities, Reclassification adjustment for (gains) losses included in net income, Before Tax Amount	(6)	(370)	(11)	121
Total securities available for sale and transferred securities, Before Tax Amount	(83,776)	20,598	(113,584)	22,971
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Before Tax Amount	1,639	1,428	3,279	2,657
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Before Tax Amount	(33)	(64)	(33)	(491)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Before Tax Amount	(9,345)	(9,345)	(18,690)	(18,690)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Before Tax Amount	1,103	1,044	2,188	2,077
Total derivatives, Before Tax Amount	(8,275)	(8,365)	(16,535)	(17,104)
Total other comprehensive income, Before Tax Amount	(90,412)	13,661	(126,840)	8,524
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Tax Expense (Benefit)	(25,909)	7,340	(33,379)	7,998
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Tax Expense (Benefit)	(3,411)		(6,372)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Tax Expense (Benefit)	(2)	(130)	(4)	42
Total securities available for sale and transferred securities, Tax Expense (Benefit)	(29,322)	7,210	(39,755)	8,040
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Tax Expense (Benefit)	574	500	1,148	930
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Tax Expense (Benefit)	(12)	(23)	(12)	(173)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Tax Expense (Benefit)	(3,270)	(3,270)	(6,541)	(6,541)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Tax Expense (Benefit)	386	365	766	727
Total derivatives, Tax Expense (Benefit)	(2,896)	(2,928)	(5,787)	(5,987)
Total other comprehensive income, Tax Expense (Benefit)	(31,644)	4,782	(44,394)	2,983
Change in net unrealized gain/loss during the period, Net of Tax	(48,116)	13,628	(61,990)	14,852
Change in net unrealized gain on securities transferred to held to maturity, Net of Tax	(6,334)		(11,832)
Reclassification adjustment for net (gains) losses included in net income, Net of Tax	(4)	(240)	(7)	79
Total securities available for sale and transferred securities, Net of Tax	(54,454)	13,388	(73,829)	14,931
Change in the net actuarial gain/loss, Net of Tax	1,065	928	2,131	1,727
Change in the accumulated gain/loss on effective cash flow hedge derivatives, Net of Tax	(21)	(41)	(21)	(318)
Interest rate swaps on variable-rate loans, Net of Tax	(6,075)	(6,075)	(12,149)	(12,149)
Interest rate swap on junior subordinated deferrable interest debentures, Net of Tax	717	679	1,422	1,350
Total derivatives, Net of Tax	(5,379)	(5,437)	(10,748)	(11,117)
Other comprehensive income (loss), net of tax	$ (58,768)	$ 8,879	$ (82,446)	$ 5,541