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Accounting Policies - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 12 Months Ended
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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

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- Definition Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 720 -SubTopic 35 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848 + Details
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- Definition The price per share of the conversion feature embedded in the debt instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6928298&loc=SL6031898-161870 + Details
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