Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 18	$ 25	$ 37	$ 46
Interest cost	31	27	67	56
Expected return on plan assets
Amortization of net actuarial loss	2	6	5	12
Accretion of prior service cost	2	(4)	(3)	(9)
Net periodic benefit (income) cost	53	54	106	105
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	137	155	273	311
Interest cost	475	426	950	857
Expected return on plan assets	(745)	(709)	(1,490)	(1,264)
Amortization of net actuarial loss	165	343	326	629
Accretion of prior service cost	(71)	(59)	(141)	(118)
Net periodic benefit (income) cost	$ (39)	$ 156	$ (82)	$ 415