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, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Amortization of pension and postretirement items:
Tax benefit	$ (3,425)		$ (2,804)		$ (15,218)		$ (12,701)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Amortization of pension and postretirement items:
Prior service cost	(67)	[1]	(107)	[1]	(132)	[1]	(213)	[1]
Net loss	(15)	[1]	(15)	[1]	(30)	[1]	(30)	[1]
Total before tax	(52)		(92)		(102)		(183)
Tax benefit	21		37		41		73
Net of tax	$ (31)		$ (55)		$ (61)		$ (110)

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