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Accounting Policies - Additional Information (Detail) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
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 $ 50.7 $ 9.7 $ 9.0
Advertising costs 3.3 1.9 1.7
Gains and losses on foreign exchange contracts $ 2.5 $ (0.9) $ (6.9)
Convertible Notes      
Summary Of Significant Accounting Policies [Line Items]      
Initial debt conversion price $ 5.48    
Shares that would be issued upon conversion 34.7    
Convertible Notes Hedge Warrant      
Summary Of Significant Accounting Policies [Line Items]      
Initial debt conversion price $ 7.67    
Shares that would be issued upon conversion 34.7