Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	$ (493,290)	$ (485,245)	$ (414,545)
Cumulative effect of change in accounting principles — equity securities, before tax	(22,795)
Unrealized holding gains (losses), net, before tax	(121,589)	(15,005)	(79,950)
Foreign currency translation adjustment, before tax	(2,817)	4,447	(4,020)
Unrealized losses on cash flow hedges, before tax	(4,965)	(12,291)
Current year benefit plans gains, before tax	19,871	9,276	14,125
Total other comprehensive income (loss) before reclassifications, before tax	(109,500)	(13,573)	(69,845)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax	4,252	3,387	3,996
Gains realized in net income, before tax	(18)	(21,279)	(30,314)
Accretion of net gain (losses) on terminated cash flow hedges, before tax	(111)	(137)	(155)
Net yield adjustment from cash flow hedges currently in effect, before tax	13,339	(3,916)
Amortization of prior service credit, before tax	(4,172)	(802)	(4,587)
Amortization of actuarial losses, before tax	42,967	28,275	30,205
Total other comprehensive income (loss), before tax	(53,243)	(8,045)	(70,700)
Ending balance, before tax	(569,328)	(493,290)	(485,245)
Beginning balance, tax	129,476	190,609	162,918
Cumulative effect of change in accounting principles — equity securities, tax	5,942
Unrealized holding gains (losses), net, tax	31,946	7,269	31,509
Foreign currency translation adjustment, tax	592	(2,206)	1,406
Unrealized losses on cash flow hedges, tax	1,306	4,837
Current year benefit plans gains, tax	(5,224)	(3,650)	(5,557)
Total other comprehensive income (loss) before reclassifications, tax	28,620	6,250	27,358
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, tax	(1,118)	(1,333)	(1,572)
Gains realized in net income, tax	4	7,195	11,925
Accretion of net gain on terminated cash flow hedges, tax	29	54	61
Net yield adjustment from cash flow hedges currently in effect, tax	(3,507)	1,541
Amortization of prior service credit, tax	1,097	315	1,805
Amortization of actuarial losses, tax	(11,296)	(11,126)	(11,886)
Total other comprehensive income (loss), tax	13,829	2,896	27,691
Reclassification of income tax effects to retained earnings, tax		(64,029)
Ending balance, tax	149,247	129,476	190,609
Beginning balance, net of tax	(363,814)	(294,636)	(251,627)
Cumulative effect of change in accounting principle — equity securities	(16,853)
Unrealized holding gains (losses), net of tax	(89,643)	(7,736)	(48,441)
Foreign currency translation adjustment	(2,225)	2,241	(2,614)
Unrealized losses on cash flow hedges, net of tax	(3,659)	(7,454)
Current year benefit plans gains, net of tax	14,647	5,626	8,568
Total other comprehensive income (loss) before reclassifications, net of tax	(80,880)	(7,323)	(42,487)
Amortization of unrealized holding losses on held-to-maturity ('HTM') securities, net of tax	3,134	2,054	2,424
Gains realized in net income, net of tax	(14)	(14,084)	(18,389)
Accretion of net gain on terminated cash flow hedges, net of tax	(82)	(83)	(94)
Net yield adjustment from cash flow hedges currently in effect, net of tax	9,832	(2,375)
Amortization of prior service credit, net of tax	(3,075)	(487)	(2,782)
Amortization of actuarial losses, net of tax	31,671	17,149	18,319
Total other comprehensive loss	(39,414)	(5,149)	(43,009)
Reclassification of income tax effects to retained earnings, net of tax		(64,029)
Ending balance, net of tax	(420,081)	(363,814)	(294,636)
Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	(59,957)
Cumulative effect of change in accounting principles — equity securities, before tax	(22,795)
Unrealized holding gains (losses), net, before tax	(121,589)
Total other comprehensive income (loss) before reclassifications, before tax	(121,589)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax	4,252
Gains realized in net income, before tax	(18)
Total other comprehensive income (loss), before tax	(117,355)
Ending balance, before tax	(200,107)	(59,957)
Cumulative effect of change in accounting principle — equity securities	(16,853)
Total other comprehensive loss	(86,523)	(19,766)	(64,406)
Reclassification of income tax effects to retained earnings, net of tax		8,065
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	(413,168)	(449,917)	(489,660)
Current year benefit plans gains, before tax	19,871	9,276	14,125
Total other comprehensive income (loss) before reclassifications, before tax	19,871	9,276	14,125
Amortization of prior service credit, before tax	(4,172)	(802)	(4,587)
Amortization of actuarial losses, before tax	42,967	28,275	30,205
Total other comprehensive income (loss), before tax	58,666	36,749	39,743
Ending balance, before tax	(354,502)	(413,168)	(449,917)
Total other comprehensive loss	43,243	22,288	24,105
Reclassification of income tax effects to retained earnings, net of tax		53,960
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	(20,165)	(8,268)	(4,093)
Foreign currency translation adjustment, before tax	(2,817)	4,447	(4,020)
Unrealized losses on cash flow hedges, before tax	(4,965)	(12,291)
Total other comprehensive income (loss) before reclassifications, before tax	(7,782)	(7,844)	(4,020)
Accretion of net gain (losses) on terminated cash flow hedges, before tax	(111)	(137)	(155)
Net yield adjustment from cash flow hedges currently in effect, before tax	13,339	(3,916)
Total other comprehensive income (loss), before tax	5,446	(11,897)	(4,175)
Ending balance, before tax	(14,719)	(20,165)	(8,268)
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	19,628	46,725	16,359
Unrealized holding gains (losses), net, before tax		(8,746)	30,366
Total other comprehensive income (loss) before reclassifications, before tax		(8,746)	30,366
Gains realized in net income, before tax		(18,351)
Total other comprehensive income (loss), before tax		(27,097)	30,366
Ending balance, before tax		19,628	46,725
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	$ (79,585)	(73,785)	62,849
Unrealized holding gains (losses), net, before tax		(6,259)	(110,316)
Total other comprehensive income (loss) before reclassifications, before tax		(6,259)	(110,316)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax		3,387	3,996
Gains realized in net income, before tax		(2,928)	(30,314)
Total other comprehensive income (loss), before tax		(5,800)	(136,634)
Ending balance, before tax		$ (79,585)	$ (73,785)