Postretirement Benefits Other Than Pensions - Funded Status of Plans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at end of year	$ 270,123	$ 251,094
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	37,428	32,508
Service cost	816	589
Interest cost	1,223	1,350
Employee contributions	415	466
Actuarial (gain) loss	(1,102)	3,317
Benefits paid	(1,550)	(2,670)
Plan amendments
Plan curtailments
Other		1,868
Benefit obligation at end of year	37,230	37,428
Fair value of plan assets at end of year
Funded status	$ (37,230)	$ (37,428)