Other Comprehensive Income (Loss) (Component of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Before Tax Amount	$ (175,061)	$ (12,450)	$ 103,044
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, Before Tax Amount	(32,207)	(33,601)	(35,441)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Before Tax Amount	(14,975)	(69)	(38)
Total securities available for sale and transferred securities	(222,243)	(46,120)	67,565
Change in the net actuarial gain/loss	1,914	(3,877)	(37,524)
Reclassification adjustment for net amortization of actuarial gain(loss) and for SERP settlement costs included in net income, before tax amount	7,274
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit)		6,995	2,687
Total defined-benefit post-retirement benefit plans	9,188	3,118	(34,837)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Before Tax Amount	0	0	(30,604)
Other comprehensive income (loss), before tax	(213,055)	(43,002)	2,124
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, Tax Expense (Benefit)	(61,271)	(4,358)	36,065
Securities available for sale and transferred securities, change in net unrealized gain on securities transfers to held-to-maturity, tax expense benefit	(11,272)	(11,760)	(12,404)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, Tax Expense (Benefit)	(5,242)	(24)	(13)
Total securities available for sale and transferred securities, Tax Expense (Benefit)	(77,785)	(16,142)	23,648
Change in the net actuarial gain/loss, Tax Expense (Benefit)	670	(1,357)	(13,133)
Reclassification adjustment for net amortization of actuarial gain(loss) and for SERP settlement costs included in net income, Tax Expense (Benefit)	2,546
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a componet of net periodic cost benefit , Tax Expense (Benefit)		2,448	940
Total defined-benefit post-retirement benefit plans, Tax Expense (Benefit)	3,216	1,091	(12,193)
Derivatives, Reclassification adjustments for (gains) losses included in net income, Interest rate swaps on variable-rate loans, Tax Expense (Benefit)			(10,711)
Total other comprehensive income, Tax Expense (Benefit)	(74,569)	(15,051)	744
Securities available for sale and transferred securities, change in net unrealized gain/loss during the period, net of tax	(113,790)	(8,092)	66,979
Securities available for sale and transferred securities. change in net unrealized gain on securities transfers to held-to-maturity, net of tax	(20,935)	(21,841)	(23,037)
Securities available for sale and securities transferred, reclassification adjustment for net (gains) losses included in net income, net of tax	(9,733)	(45)	(25)
Total securities available for sale and transferred securities, net of tax	(144,458)	(29,978)	43,917
Change in the net actuarial gain/loss, Net of Tax Amount	1,244	(2,520)	(24,391)
Reclassification adjustment for net amortization of actuarial gain (loss) and for SERP settlement costs included in net income, Net of Tax Amount	4,728
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a componet of net periodic cost (benefit), Net of Tax Amount		4,547	1,747
Total defined-benefit post-retirement benefit plans, Net of Tax Amount	5,972	2,027	(22,644)
Derivatives, reclassification adjustment for (gains) losses included in net income, interest rate swaps on variable-rate loans, net of tax			(19,893)
Other comprehensive income (loss), net of tax	$ (138,486)	$ (27,951)	$ 1,380