Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (251,627)	$ (180,994)
Net gain (loss) during period	$ 49,168	$ (65,011)	150,606	(36,508)
Ending balance	(101,021)	$ (217,502)	(101,021)	$ (217,502)
Investment Securities With OTTI [Member] | Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			9,921
Net gain (loss) during period			5,616
Ending balance	15,537		15,537
Investment Securities All Other [Member] | Investment Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			38,166
Net gain (loss) during period			138,848
Ending balance	177,014		177,014
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(296,979)
Net gain (loss) during period			7,807
Ending balance	(289,172)		(289,172)
Accumulated Other Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(2,735)
Net gain (loss) during period			(1,665)
Ending balance	$ (4,400)		$ (4,400)