Accounting Policies - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary Of Significant Accounting Policies [Line Items]
Depreciation over life to cost of revenues and selling and administrative expenses, years	6 years
Net book value of internally manufactured test systems sold	$ 11.4	$ 50.7	$ 9.7
Advertising costs	6.4	3.3	1.9
Gains (losses) on foreign currency transactions	$ 8.0	$ 2.5	$ 0.9
Convertible Notes
Summary Of Significant Accounting Policies [Line Items]
Initial debt conversion price	$ 5.48		$ 5.48
Shares that would be issued upon conversion	34.7		34.7
Convertible Notes Hedge Warrant
Summary Of Significant Accounting Policies [Line Items]
Initial debt conversion price	$ 7.67		$ 7.67
Shares that would be issued upon conversion	34.7		34.7