Other Comprehensive Income (Loss) (Component of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, before tax amount	$ (231,355)	$ 427,331	$ 418,556
Securities available for sale and transferred securities, Change in net unrealized gain on securities transferred to held to maturity, before tax amount	(971)	(1,256)	(1,292)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, before tax amount	(69)	(108,989)	(293)
Total securities available for sale and transferred securities before tax amount	(232,395)	317,086	416,971
Change in the net actuarial gain/loss before tax amount	16,593	(11,518)	(3,644)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a component of net periodic cost (benefit) before tax amount	6,116	5,319	5,623
Total defined-benefit post-retirement benefit plans	22,709	(6,199)	1,979
Other comprehensive income (loss), before tax	(209,686)	310,887	418,950
Securities available for sale and transferred securities, Change in net unrealized gain/loss during the period, tax expense (benefit)	(48,585)	89,741	87,897
Securities available for sale and transferred securities, change in net unrealized gain on securities transfers to held-to-maturity, tax expense benefit	(204)	(264)	(271)
Securities available for sale and transferred securities, Reclassification adjustment for net (gains) losses included in net income, tax expense (benefit)	(14)	(22,888)	(62)
Total securities available for sale and transferred securities, tax expense (benefit)	(48,803)	66,589	87,564
Change in the net actuarial gain/loss, tax expense (benefit)	3,485	(2,419)	(765)
Reclassification adjustment for net amortization of actuarial gain/loss included in net income as a componet of net periodic cost (benefit) , tax expense (benefit)	1,284	1,117	1,181
Total defined-benefit post-retirement benefit plans, tax expense (benefit)	4,769	(1,302)	416
Total other comprehensive income, tax expense (benefit)	(44,034)	65,287	87,980
Securities available for sale and transferred securities, change in net unrealized gain/loss during the period, net of tax amount	(182,770)	337,590	330,659
Securities available for sale and transferred securities. change in net unrealized gain on securities transfers to held-to-maturity, net of tax amount	(767)	(992)	(1,021)
Securities available for sale and securities transferred, reclassification adjustment for net (gains) losses included in net income, net of tax amount	(55)	(86,101)	(231)
Total securities available for sale and transferred securities, net of tax amount	(183,592)	250,497	329,407
Change in the net actuarial gain/loss, net of tax amount	13,108	(9,099)	(2,879)
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	4,832	4,202	4,442
Total defined-benefit post-retirement benefit plans, net of tax amount	17,940	(4,897)	1,563
Other comprehensive income (loss), net of tax	$ (165,652)	$ 245,600	$ 330,970