Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net (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	$ (180,994)	$ (64,159)
Net gain (loss) during period	28,503	38,898
Ending balance	(152,491)	(25,261)
Investment Securities With OTTI [Member] | Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	4,518
Net gain (loss) during period	4,898
Ending balance	9,416
Investment Securities All Other [Member] | Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	122,683
Net gain (loss) during period	20,441
Ending balance	143,124
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(305,589)
Net gain (loss) during period	4,677
Ending balance	(300,912)
Accumulated Other Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(2,606)
Net gain (loss) during period	(1,513)
Ending balance	$ (4,119)