Postretirement Benefits Other Than Pensions - Net Postretirement Benefit Expense Components (Detail) (Other Postretirement Benefit Plans, Defined Benefit [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost		$ 42	$ 46
Interest cost	194	790	1,052
Amortization of net actuarial loss	477	491	2
Amortization of prior service credit	(1,331)	(682)	(678)
Curtailment gain		(310)
Net postretirement benefit expense	$ (660)	$ 331	$ 422