Comprehensive Income - Accumulated Other Comprehensive Income (Loss), Net Consisted of Unrealized Gains (Losses) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			$ (240,264)	$ (356,441)
Net gain (loss) during period	29,709	47,774	42,202	126,366
Ending Balance	(198,062)	(230,075)	(198,062)	(230,075)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(276,771)
Net gain (loss) during period			15,273
Ending Balance	(261,498)		(261,498)
Accumulated Other Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(284)
Net gain (loss) during period			205
Ending Balance	(79)		(79)
Investment Securities [Member] | Investment Securities With OTTI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			(55,790)
Net gain (loss) during period			67,293
Ending Balance	11,503		11,503
Investment Securities [Member] | Investment Securities All Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance			92,581
Net gain (loss) during period			(40,569)
Ending Balance	$ 52,012		$ 52,012