Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	$ (485,245)	$ (414,545)
Unrealized holding gains (losses), before tax	(3,015)	159,290
Foreign currency translation adjustment, before tax	732	(83)
Total other comprehensive income (loss) before reclassifications, before tax	(2,283)	159,207
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities, before tax	787	968
Gains (losses) realized in net income, before tax		(4)
Accretion of net gain (losses) on terminated cash flow hedges, before tax	(39)	(39)
Amortization of prior service credit, before tax	(225)	(1,175)
Amortization of actuarial losses, before tax	6,775	8,300
Total reclassifications, before tax	7,298	8,050
Total gain (loss) during the period, before tax	5,015	167,257
Ending balance, before tax	(480,230)	(247,288)
Beginning balance, tax	190,609	162,918
Unrealized holding gains (losses), tax	1,182	(62,680)
Foreign currency translation adjustment, tax	(256)	30
Total other comprehensive income (loss) before reclassifications, tax	926	(62,650)
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities, tax	(310)	(381)
Gains (losses) realized in net income, tax		1
Accretion of net gain (losses) on terminated cash flow hedges, tax	16	15
Amortization of prior service credit, tax	88	462
Amortization of actuarial losses, tax	(2,666)	(3,266)
Total reclassifications, tax	(2,872)	(3,169)
Total gain (loss) during the period, tax	(1,946)	(65,819)
Ending balance, tax	188,663	97,099
Beginning balance, net of tax	(294,636)	(251,627)
Unrealized holding gains (losses), net	(1,833)	96,610
Foreign currency translation adjustment, net of tax	476	(53)
Total other comprehensive income (loss) before reclassifications, net of tax	(1,357)	96,557
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities, net of tax	477	587
Gains (losses) realized in net income, net of tax		(3)
Accretion of net gain on terminated cash flow hedges, net of tax	(23)	(24)
Amortization of prior service credit, net of tax	(137)	(713)
Amortization of actuarial losses, net of tax	4,109	5,034
Total reclassifications, net of tax	4,426	4,881
Total other comprehensive income	3,069	101,438
Ending balance, net of tax	(291,567)	(150,189)
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	46,725	16,359
Unrealized holding gains (losses), before tax	(8,628)	(370)
Total other comprehensive income (loss) before reclassifications, before tax	(8,628)	(370)
Total gain (loss) during the period, before tax	(8,628)	(370)
Ending balance, before tax	38,097	15,989
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	(73,785)	62,849
Unrealized holding gains (losses), before tax	5,613	159,660
Total other comprehensive income (loss) before reclassifications, before tax	5,613	159,660
Amortization of unrealized holding losses on held-to-maturity (“HTM”) securities, before tax	787	968
Gains (losses) realized in net income, before tax		(4)
Total reclassifications, before tax	787	964
Total gain (loss) during the period, before tax	6,400	160,624
Ending balance, before tax	(67,385)	223,473
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	(449,917)	(489,660)
Amortization of prior service credit, before tax	(225)	(1,175)
Amortization of actuarial losses, before tax	6,775	8,300
Total reclassifications, before tax	6,550	7,125
Total gain (loss) during the period, before tax	6,550	7,125
Ending balance, before tax	(443,367)	(482,535)
Total other comprehensive income	3,972
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	(8,268)	(4,093)
Foreign currency translation adjustment, before tax	732	(83)
Total other comprehensive income (loss) before reclassifications, before tax	732	(83)
Accretion of net gain (losses) on terminated cash flow hedges, before tax	(39)	(39)
Total reclassifications, before tax	(39)	(39)
Total gain (loss) during the period, before tax	693	(122)
Ending balance, before tax	$ (7,575)	$ (4,215)