Postretirement Benefits Other than Pensions - Net Periodic Pension and Postretirement Benefit (Income) Expense (Detail) - Other Postretirement Benefit Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 127	$ 221	$ 194
Amortization of net actuarial loss	255	445	477
Amortization of prior service credit	(1,314)	(1,314)	(1,331)
Total net periodic pension (income) expense	$ (932)	$ (648)	$ (660)