Retirement Plans and Other Postretirement Benefits - Reconciliation of Beginning and Ending Balances for Measurements in Hierarchy Level 3 (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning Balance	$ 4,035	$ 4,339
Total Unrealized (Losses) or Gains	0	0
Total Realized Gains or (Losses)	0	0
Purchases	1,805	595
Maturities/ Redemptions	(1,085)	(899)
Ending Balance	4,755	4,035
Certificates of Deposit [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Beginning Balance	4,035	4,339
Total Unrealized (Losses) or Gains	0	0
Total Realized Gains or (Losses)	0	0
Purchases	1,805	595
Maturities/ Redemptions	(1,085)	(899)
Ending Balance	$ 4,755	$ 4,035