Postretirement Benefits Other Than Pensions - Change in Benefit Obligation of Postretirement Plans to Accrued Postretirement Liability (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Amendments	$ (2,828)	$ (16,508)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Benefit obligation at beginning of year	8,747	24,621
Service cost		42	46
Interest cost	194	790	1,052
Actuarial loss	319	958
Amendments	(2,828)	(16,508)
Benefits paid	(584)	(1,156)
Benefit obligation at end of year	$ 5,848	$ 8,747	$ 24,621