Segment And Geographic Information - Schedule of Geographic Revenue Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Foreign revenues	$ 63,954	$ 91,322	$ 129,486	$ 158,577
Concentration risk, percentage (or more)	100.00%	100.00%	100.00%	100.00%
Customer One | Total Revenue | Customer Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk, percentage (or more)	10.00%	10.00%	10.00%	10.00%
Customer One | Total Accounts Receivable | Customer Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk, percentage (or more)			10.00%		10.00%
Customer Two | Total Revenue | Customer Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk, percentage (or more)		10.00%		10.00%
Customer Two | Total Accounts Receivable | Customer Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk, percentage (or more)					10.00%
Customer Three | Total Revenue | Customer Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk, percentage (or more)		10.00%		10.00%
Customer Three | Total Accounts Receivable | Customer Concentration Risk
Revenues from External Customers and Long-Lived Assets [Line Items]
Concentration risk, percentage (or more)					10.00%
Japan
Revenues from External Customers and Long-Lived Assets [Line Items]
Foreign revenues	$ 18,199	$ 20,169	$ 37,543	$ 34,059
Concentration risk, percentage (or more)	29.00%	22.00%	29.00%	22.00%
Korea
Revenues from External Customers and Long-Lived Assets [Line Items]
Foreign revenues	$ 17,459	$ 14,103	$ 31,887	$ 20,990
Concentration risk, percentage (or more)	27.00%	15.00%	25.00%	13.00%
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Foreign revenues	$ 13,952	$ 33,680	$ 25,579	$ 67,086
Concentration risk, percentage (or more)	22.00%	37.00%	20.00%	42.00%
Europe and Middle East
Revenues from External Customers and Long-Lived Assets [Line Items]
Foreign revenues	$ 10,925	$ 5,070	$ 16,134	$ 6,790
Concentration risk, percentage (or more)	17.00%	6.00%	12.00%	4.00%
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Foreign revenues	$ 1,491	$ 3,599	$ 15,635	$ 6,653
Concentration risk, percentage (or more)	2.00%	4.00%	12.00%	4.00%
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Foreign revenues	$ 1,928	$ 14,701	$ 2,708	$ 22,999
Concentration risk, percentage (or more)	3.00%	16.00%	2.00%	15.00%