Accumulated Other Comprehensive Income (Loss) - Reclassifications of Accumulated Other Comprehensive Loss (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
Amortization of pension and postretirement items:
Tax benefit	$ 2,916		$ 2,083	$ 15,617		$ 12,641
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Amortization of pension and postretirement items:
Prior service cost	15	[1]		45	[1]
Net loss	107	[1]		320	[1]
Total before tax	(92)			(275)
Tax benefit	(37)			(110)
Net of tax	$ (55)			$ (165)

[1] These amounts are included in the computation of net periodic costs (benefits). See Note 9, “Employee Benefit Plans,” for additional details.