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, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Amortization of pension and postretirement items:
Tax benefit	$ (2,085)		$ (2,916)		$ (17,303)		$ (15,617)
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]	15	[1]	44	[1]	45	[1]
Net loss	66	[1]	107	[1]	198	[1]	320	[1]
Total before tax	(51)		(92)		(154)		(275)
Tax benefit	21		37		62		110
Net of tax	$ (30)		$ (55)		$ (92)		$ (165)

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