Postretirement Benefits Other Than Pensions - Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 10,400	$ 12,969	$ 12,129
Net Periodic Benefit Cost
Defined Benefit Plan Disclosure [Line Items]
Service and interest cost	2,039	1,939	789
Prior service cost	26	26	(66)
Unrecognized net loss	298	129	494
Other	2,286	1,868	16,012	[1]
Net periodic benefit cost	$ 4,649	$ 3,962	$ 17,229

[1] This amount in 2011 represents an increase in our net periodic benefit cost for the year ended December 31, 2011 as a result of identifying groups of employees who were eligible to receive other postretirement benefits that had historically been excluded from our benefit plan valuations.