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, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	$ (414,545)	$ (297,843)	$ (105,797)
Unrealized holding gains (losses), before tax	(79,950)	(133,702)	150,187
Foreign currency translation adjustment, before tax	(4,020)	(1,323)	(4,039)
Unrealized Gains (losses) on cash flow hedges, before tax		1,453	(165)
Current year benefit plans gains (losses), before tax	14,125	(24,200)	(347,993)
Total other comprehensive income (loss) before reclassifications, before tax	(69,845)	(157,772)	(202,010)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax	3,996	3,514	3,374
Gains (losses) realized in net income, before tax	(30,314)	130
Accretion of net gain (losses) on terminated cash flow hedges, before tax	(155)	(141)	7
Amortization of prior service credit, before tax	(4,587)	(7,364)	(7,911)
Amortization of actuarial losses, before tax	30,205	44,931	14,494
Total reclassifications, before tax	(855)	41,070	9,964
Total gain (loss) during the period, before tax	(70,700)	(116,702)	(192,046)
Ending balance, before tax	(485,245)	(414,545)	(297,843)
Beginning balance, tax	162,918	116,849	41,638
Unrealized holding gains (losses), tax	31,509	52,376	(58,962)
Foreign currency translation adjustment, tax	1,406	398	1,432
Unrealized Gains (losses) on cash flow hedges, tax		(572)	65
Current year benefit plans gains (losses), tax	(5,557)	8,612	136,587
Total other comprehensive income (loss) before reclassifications, tax	27,358	60,814	79,122
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, tax	(1,572)	(1,383)	(1,324)
Gains (losses) realized in net income, tax	11,925	(49)
Accretion of net gain (losses) on terminated cash flow hedges, tax	61	56	(3)
Amortization of prior service credit, tax	1,805	2,620	3,105
Amortization of actuarial losses, tax	(11,886)	(15,989)	(5,689)
Total reclassifications, tax	333	(14,745)	(3,911)
Total gain (loss) during the period, tax	27,691	46,069	75,211
Ending balance, tax	190,609	162,918	116,849
Beginning balance, net of tax	(251,627)	(180,994)	(64,159)
Unrealized holding gains (losses), net of tax	(48,441)	(81,326)	91,225
Foreign currency translation adjustment, net of tax	(2,614)	(925)	(2,607)
Unrealized Gains (losses) on cash flow hedges, net of tax		881	(100)
Current year benefit plans gains (losses), net of tax	8,568	(15,588)	(211,406)
Total other comprehensive income (loss) before reclassifications, net of tax	(42,487)	(96,958)	(122,888)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, net of tax	2,424	2,131	2,050
Gains (losses) realized in net income, net of tax	(18,389)	81
Accretion of net gain on terminated cash flow hedges, net of tax	(94)	(85)	4
Amortization of prior service credit, net of tax	(2,782)	(4,744)	(4,806)
Amortization of actuarial losses, net of tax	18,319	28,942	8,805
Total reclassifications, net of tax	(522)	26,325	6,053
Total other comprehensive loss	(43,009)	(70,633)	(116,835)
Ending balance, net of tax	(294,636)	(251,627)	(180,994)
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	16,359	7,438	37,255
Unrealized holding gains (losses), before tax	30,366	8,921	(29,818)
Total other comprehensive income (loss) before reclassifications, before tax	30,366	8,921	(29,818)
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax			1
Total reclassifications, before tax			1
Total gain (loss) during the period, before tax	30,366	8,921	(29,817)
Ending balance, before tax	46,725	16,359	7,438
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	62,849	201,828	18,450
Unrealized holding gains (losses), before tax	(110,316)	(142,623)	180,005
Total other comprehensive income (loss) before reclassifications, before tax	(110,316)	(142,623)	180,005
Amortization of unrealized holding losses on held-to-maturity ("HTM") securities, before tax	3,996	3,514	3,373
Gains (losses) realized in net income, before tax	(30,314)	130
Total reclassifications, before tax	(26,318)	3,644	3,373
Total gain (loss) during the period, before tax	(136,634)	(138,979)	183,378
Ending balance, before tax	(73,785)	62,849	201,828
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	(489,660)	(503,027)	(161,617)
Current year benefit plans gains (losses), before tax	14,125	(24,200)	(347,993)
Total other comprehensive income (loss) before reclassifications, before tax	14,125	(24,200)	(347,993)
Amortization of prior service credit, before tax	(4,587)	(7,364)	(7,911)
Amortization of actuarial losses, before tax	30,205	44,931	14,494
Total reclassifications, before tax	25,618	37,567	6,583
Total gain (loss) during the period, before tax	39,743	13,367	(341,410)
Ending balance, before tax	(449,917)	(489,660)	(503,027)
Total other comprehensive loss	24,105	8,610	(207,407)
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, before tax	(4,093)	(4,082)	115
Foreign currency translation adjustment, before tax	(4,020)	(1,323)	(4,039)
Unrealized Gains (losses) on cash flow hedges, before tax		1,453	(165)
Total other comprehensive income (loss) before reclassifications, before tax	(4,020)	130	(4,204)
Accretion of net gain (losses) on terminated cash flow hedges, before tax	(155)	(141)	7
Total reclassifications, before tax	(155)	(141)	7
Total gain (loss) during the period, before tax	(4,175)	(11)	(4,197)
Ending balance, before tax	$ (8,268)	$ (4,093)	$ (4,082)