Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 137	$ 155	$ 410	$ 466
Interest cost	476	427	1,426	1,284
Expected return on plan assets	(746)	(630)	(2,236)	(1,894)
Amortization of net actuarial loss	164	314	490	943
Accretion of prior service cost	(71)	(58)	(212)	(176)
Net periodic benefit (income) cost	(40)	208	(122)	623
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	19	23	56	69
Interest cost	32	30	99	86
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss	4	6	9	18
Accretion of prior service cost	(1)	(6)	(4)	(15)
Net periodic benefit (income) cost	$ 54	$ 53	$ 160	$ 158