Other Comprehensive Income (Loss) (Component of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Before Tax Amount	$ (12,450)	$ 103,044	$ (115,245)
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Before Tax Amount	(33,601)	(35,441)	(35,682)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Before Tax Amount	(69)	(38)	(1,176)
Total securities available for sale and transferred securities	(46,120)	67,565	(152,103)
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Before Tax Amount	3,118	(34,837)	35,293
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Before Tax Amount	0	0	(49)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Before Tax Amount	0	(30,604)	(37,380)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Before Tax Amount	0	0	4,064
Total derivatives	0	(30,604)	(33,365)
Other comprehensive income (loss), before tax	(43,002)	2,124	(150,175)
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Tax Expense (Benefit)	(4,358)	36,065	(40,335)
Securities available for sale and transferred securities, change in net unrealized gain on securities transfers to held-to-maturity, tax expense benefit	(11,760)	(12,404)	(12,489)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Tax Expense (Benefit)	(24)	(13)	(412)
Total securities available for sale and transferred securities, Tax Expense (Benefit)	(16,142)	23,648	(53,236)
Defined-benefit post-retirement benefit plans, Change in the net actuarial gain/loss, Tax Expense (Benefit)	1,091	(12,193)	12,353
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, Tax Expense (Benefit)			(17)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Tax Expense (Benefit)		(10,711)	(13,083)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swap on junior subordinated deferrable interest debentures, Tax Expense (Benefit)			1,422
Derivatives, Total derivatives, Tax Expense, (Benefit)			(11,678)
Total other comprehensive income, Tax Expense (Benefit)	(15,051)	744	(52,561)
Securities available for sale and transferred securities, change in net unrealized gain/loss during the period, net of tax	(8,092)	66,979	(74,910)
Securities available for sale and transferred securities. change in net unrealized gain on securities transfers to held-to-maturity, net of tax	(21,841)	(23,037)	(23,193)
Securities available for sale and securities transferred, reclassification adjustment for net (gains) losses included in net income, net of tax	(45)	(25)	(764)
Total securities available for sale and transferred securities, net of tax	(29,978)	43,917	(98,867)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), Net of Tax	2,027	(22,644)	22,940
Derivatives, Change in the accumulated gain/loss on effective cash flow hedge derivatives, net of tax			(32)
Derivatives, reclassification adjustment for (gains) losses included in net income, interest rate swaps on variable-rate loans, net of tax		(19,893)	(24,297)
Derivatives, reclassification adjustment for (gains) losses included in net income, interest rate swap on junior subordinated deferrable interest debentures, net of tax			2,642
Derivatives, Total derivatives, net of tax			(21,687)
Other comprehensive income (loss), net of tax	$ (27,951)	$ 1,380	$ (97,614)