Property, Plant and Equipment - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Abstract]
Depreciation	$ 76,883	$ 78,482	$ 71,504
Capital lease obligations	$ 1,000	$ 1,100