Comprehensive Income - Components of Other Comprehensive Income (Loss) and Amounts Reclassified from Accumulated Other Comprehensive Income (Loss) to Net Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (297,843)	$ (105,797)
Unrealized holding gains, net	40,074	62,087
Foreign currency translation adjustment	(3,732)	(234)
Gains on cash flow hedges	1,453
Total other comprehensive income before reclassifications	37,795	61,853
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	739	825
Losses realized in net income	98
Accretion of losses on terminated cash flow hedges	(24)
Amortization of prior service credit	(1,875)	(2,000)
Amortization of actuarial losses	11,200	3,350
Total reclassifications	10,138	2,175
Total gain (loss) during the period	47,933	64,028
Ending balance	(249,910)	(41,769)
Beginning balance	116,849	41,638
Unrealized holding gains, net	(15,247)	(24,374)
Foreign currency translation adjustment	1,348	98
Gains on cash flow hedges	(568)
Total other comprehensive income before reclassifications	(14,467)	(24,276)
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	(289)	(324)
Losses realized in net income	(36)
Accretion of losses on terminated cash flow hedges	10
Amortization of prior service credit	934	785
Amortization of actuarial losses	(5,582)	(1,315)
Total reclassifications	(4,963)	(854)
Total gain (loss) during the period	(19,430)	(25,130)
Ending balance	97,419	16,508
Beginning balance	(180,994)	(64,159)
Unrealized holding gains, net	24,827	37,713
Foreign currency translation adjustment	(2,384)	(136)
Gains on cash flow hedges	885
Total other comprehensive income before reclassifications	23,328	37,577
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	450	501
Losses realized in net income	62
Accretion of gain on terminated cash flow hedges	(14)
Amortization of prior service credit	(941)	(1,215)
Amortization of actuarial losses	5,618	2,035
Total reclassifications	5,175	1,321
Total gain (loss) during the period	28,503	38,898
Ending balance	(152,491)	(25,261)
Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	7,438	37,255
Unrealized holding gains, net	8,011	19,968
Total other comprehensive income before reclassifications	8,011	19,968
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities		2
Total reclassifications		2
Total gain (loss) during the period	8,011	19,970
Ending balance	15,449	57,225
Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	201,828	18,450
Unrealized holding gains, net	32,063	42,119
Total other comprehensive income before reclassifications	32,063	42,119
Accretion of unrealized holding losses on held-to-maturity ("HTM") securities	739	823
Losses realized in net income	98
Total reclassifications	837	823
Total gain (loss) during the period	32,900	42,942
Ending balance	234,728	61,392
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(503,027)	(161,617)
Amortization of prior service credit	(1,875)	(2,000)
Amortization of actuarial losses	11,200	3,350
Total reclassifications	9,325	1,350
Total gain (loss) during the period	9,325	1,350
Ending balance	(493,702)	(160,267)
Beginning balance	(305,589)
Total gain (loss) during the period	4,677
Ending balance	(300,912)
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4,082)	115
Foreign currency translation adjustment	(3,732)	(234)
Gains on cash flow hedges	1,453
Total other comprehensive income before reclassifications	(2,279)	(234)
Accretion of losses on terminated cash flow hedges	(24)
Total reclassifications	(24)
Total gain (loss) during the period	(2,303)	(234)
Ending balance	$ (6,385)	$ (119)