Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Taxes
Unrecognized tax benefits	$ 4,500		$ 4,500
Unrecognized tax benefits would impact the effective tax rate	4,000		4,000
Interest accrued	700		$ 700
Effective tax rate from operations			(3.80%)	17.80%
(Benefit from) provision for income taxes	(1,240)	$ 2,536	$ (699)	$ 9,463
Effective U.S corporate tax rate			21.00%		35.00%
Transition tax					$ 40,300
Measurement period adjustment to reduce transition tax	3,100
Provisional estimate for transition tax	37,200		$ 37,200
Transition tax paid	8,300		8,300
Other Long-term Liabilities
Income Taxes
Transition tax	28,900		28,900		36,800
U.S
Income Taxes
Cash and cash equivalents and short-term investments	297,000		$ 297,000		293,800
U.S | Earliest Tax Year
Income Taxes
Tax years subject to examination			2014
Germany | Earliest Tax Year
Income Taxes
Tax years subject to examination			2016
Poland | Earliest Tax Year
Income Taxes
Tax years subject to examination			2013
Italy | Earliest Tax Year
Income Taxes
Tax years subject to examination			2013
China | Earliest Tax Year
Income Taxes
Tax years subject to examination			2013
Spain | Earliest Tax Year
Income Taxes
Tax years subject to examination			2014
United Kingdom | Earliest Tax Year
Income Taxes
Tax years subject to examination			2016
Foreign
Income Taxes
Cash and cash equivalents and short-term investments	$ 402,200		$ 402,200		$ 381,400