Pension and Postretirement Benefits Other Than Pension Plans - Additional Information (Detail) - Pension Plan [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Net settlement loss	$ 1,218	$ 1,567	$ 1,218	$ 1,567
Discount rate	3.30%		3.30%		3.70%
Decrease in pension plan liability			$ (300)