Inventories, Net - Allowance for Excess and Obsolete Inventory (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventory Valuation And Obsolescence [Roll Forward]
Balance at beginning of year	$ 33,532	$ 21,537
Provision	21,369	32,072	$ 8,800
Charges processed	(20,499)	(20,077)
Balance at end of year	$ 34,402	$ 33,532	$ 21,537