Components of Net Periodic Benefit Cost - Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	$ 0	$ 0
Interest cost	352	318
Expected return on plan assets	(894)	(792)
Amortization of prior service cost	0	0
Amortization of the net loss (gain)	93	338
Net periodic benefit cost (increase)	(449)	(136)
Other post-retirement benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Service cost	42	60
Interest cost	272	245
Expected return on plan assets	0	0
Amortization of prior service cost	(1)	(1)
Amortization of the net loss (gain)	(51)	4
Net periodic benefit cost (increase)	$ 262	$ 308