Accumulated Other Comprehensive Income (Loss) - Reclassifications of Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Amortization of pension and postretirement items:
Tax benefit	$ 2,804		$ 3,307	$ 12,701		$ 10,558
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]		30	[1]
Net loss	107	[1]		213	[1]
Total before tax	(92)			(183)
Tax benefit	(37)			(73)
Net of tax	$ (55)			$ (110)

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