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Convertible Notes, Other Debts And Finance Lease - Narratives (Details) | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |
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Jun. 26, 2020 USD ($) | Jun. 26, 2020 EUR (€) | Apr. 30, 2020 CHF (SFr) | Sep. 25, 2020 USD ($) $ / shares | Jun. 26, 2020 USD ($) | Sep. 27, 2019 USD ($) | Sep. 25, 2020 USD ($) day $ / shares | Sep. 27, 2019 USD ($) | Dec. 31, 2019 USD ($) $ / shares | Dec. 31, 2015 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Common stock, par value | $ / shares |  |  |  |  | $ 0.001 |  |  | $ 0.001 |  | $ 0.001 |
Fair value of Convertible Senior Notes due 2022 used to settle Convertible Senior Notes due 2020 |  |  |  |  |  |  |  | $ 44,357,000 |  |  |
Loss on debt extinguishment |  |  |  |  | $ 0 |  | $ 5,695,000 | 834,000 | $ 5,695,000 |  |
Financing from French government agencies related to various government incentive programs (1) | [1] |  |  |  | 14,533,000 |  |  | 14,533,000 |  | $ 16,566,000 |
Letters of Credit Outstanding, Amount |  |  |  |  | 2,700,000 |  |  | 2,700,000 |  | 2,700,000 |
Relief loans (2) | [2] |  |  |  | $ 6,375,000 |  |  | $ 6,375,000 |  |  |
Société Générale S.A. [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  | 0.51% |  |  | 0.51% |  |  |
Proceeds from Loans | € |  |  | € 5,000,000 |  |  |  |  |  |  |  |
Debt Instrument, Term |  |  |  |  |  |  |  | 12 months |  |  |
Relief loans (2) |  |  |  |  | $ 5,800,000 |  |  | $ 5,800,000 |  |  |
UBS Switzerland AG [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  | 0.00% |  |  | 0.00% |  |  |
Proceeds from Loans | SFr |  |  |  | SFr 500,000 |  |  |  |  |  |  |
Debt Instrument, Term |  |  |  |  |  |  |  | 5 years |  |  |
Relief loans (2) |  |  |  |  | $ 500,000 |  |  | $ 500,000 |  |  |
TVN [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Income Taxes Receivable |  |  |  |  | $ 19,500,000 |  |  | $ 19,500,000 |  |  |
Loans Backed By French Research And Development Tax Credit Receivables [Member] | TVN [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  | 0.60% |  |  | 0.60% |  |  |
Financing from French government agencies related to various government incentive programs (1) | [1] |  |  |  | $ 13,000,000.0 |  |  | $ 13,000,000.0 |  | 15,100,000 |
Debt Instrument, Basis Spread on Variable Rate |  |  |  |  |  |  |  | 1.30% |  |  |
Loans From French Government For R&D Innovation Projects [Member] | TVN [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Financing from French government agencies related to various government incentive programs (1) | [1] |  |  |  | $ 1,500,000 |  |  | $ 1,500,000 |  |  |
Revolving Credit Facility [Member] | JPMorgan Chase Bank, N.A. [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  | 1.25% |  |  | 1.25% |  |  |
Line of Credit Facility, Current Borrowing Capacity |  |  |  |  | $ 0 |  |  | $ 0 |  | 0 |
Letters of Credit Outstanding, Amount |  |  |  |  | 200,000 |  |  | 200,000 |  | 200,000 |
Revolving Credit Facility [Member] | Silicon Valley Bank [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Letters of Credit Outstanding, Amount |  |  |  |  | $ 2,400,000 |  |  | $ 2,400,000 |  |  |
Convertible Note due 2022 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  | 4.375% |  |  | 4.375% | 4.375% |  | 4.375% |  |  |
Principal amount |  | $ 37,700,000 |  |  | $ 37,707,000 | $ 37,700,000 |  | $ 37,707,000 |  |  |
Common stock, par value | $ / shares |  |  |  |  | $ 0.001 |  |  | $ 0.001 |  |  |
Debt Instrument, Convertible, Conversion Ratio |  |  |  |  |  |  |  | 173.9978 |  |  |
Debt Conversion, Converted Instrument, Amount |  |  |  |  |  |  |  | $ 1,000 |  |  |
Debt Instrument, Convertible, Conversion Price | $ / shares |  |  |  |  | $ 5.75 |  |  | $ 5.75 |  |  |
Carrying amount of equity component |  | 8,300,000 |  |  |  | 8,300,000 |  |  |  |  |
Fair Value of Liability Component - Convertible Notes |  | 36,000,000.0 |  |  |  | 36,000,000.0 |  |  |  |  |
Debt Instrument, Unamortized Discount |  | 1,700,000 |  |  | $ 1,521,000 | 1,700,000 |  | $ 1,521,000 |  |  |
Non-cash Exchange of Convertible Notes - Value of Consideration Received |  | 37,700,000 |  |  |  |  |  |  |  |  |
Convertible Note due 2022 | Stock price greater or equal 130 percent of Note Conversion Price [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Trading Days | day |  |  |  |  |  |  |  | 20 |  |  |
Debt Instrument, Convertible, Threshold Consecutive Trading Days | day |  |  |  |  |  |  |  | 30 |  |  |
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger |  |  |  |  |  |  |  | 130.00% |  |  |
Convertible Note due 2022 | Note price less than 98 percent of stock price times conversion rate [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Trading Days | day |  |  |  |  |  |  |  | 5 |  |  |
Debt Instrument, Convertible, Threshold Consecutive Trading Days | day |  |  |  |  |  |  |  | 5 |  |  |
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger |  |  |  |  |  |  |  | 98.00% |  |  |
Convertible Note due 2024 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  | 2.00% |  | 2.00% | 2.00% | 2.00% |  |
Principal amount |  |  |  |  | $ 115,500,000 |  | $ 115,500,000 | $ 115,500,000 | $ 115,500,000 | 115,500,000 |
Common stock, par value | $ / shares |  |  |  |  | $ 0.001 |  |  | $ 0.001 |  |  |
Debt Instrument, Convertible, Conversion Ratio |  |  |  |  |  |  |  | 115.5001 |  |  |
Debt Conversion, Converted Instrument, Amount |  |  |  |  |  |  |  | $ 1,000 |  |  |
Debt Instrument, Convertible, Conversion Price | $ / shares |  |  |  |  | $ 8.66 |  |  | $ 8.66 |  |  |
Carrying amount of equity component |  |  |  |  |  |  | 24,900,000 |  | 24,900,000 |  |
Debt Instrument, Unamortized Discount |  |  |  |  | $ 20,415,000 |  |  | $ 20,415,000 |  | 23,652,000 |
Convertible Note due 2020 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  | 4.00% |  |  | 4.00% |  |  | 4.00%
Principal amount |  |  |  |  | $ 8,053,000 |  |  | $ 8,053,000 |  | 45,785,000 | $ 128,250,000
Debt Instrument, Convertible, Conversion Ratio |  |  |  |  |  |  |  | 173.9978 |  |  |
Debt Conversion, Converted Instrument, Amount |  |  |  |  |  |  |  | $ 1,000 |  |  |
Debt Instrument, Convertible, Conversion Price | $ / shares |  |  |  |  | $ 5.75 |  |  | $ 5.75 |  |  |
Carrying amount of equity component |  |  |  |  |  |  |  |  |  |  | $ 26,100,000
Debt Instrument, Unamortized Discount |  |  |  |  | $ 72,000 |  |  | $ 72,000 |  | $ 2,151,000 |
Debt Instrument, Repurchase Amount |  |  |  |  |  |  | 109,600,000 |  | 109,600,000 |  |
Non-cash Exchange of Convertible Notes - Value of Consideration Given |  | 37,700,000 |  |  |  |  |  |  |  |  |
Convertible Note due 2020 | Stock price greater or equal 130 percent of Note Conversion Price [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Convertible, Threshold Trading Days | day |  |  |  |  |  |  |  | 20 |  |  |
Debt Instrument, Convertible, Threshold Consecutive Trading Days | day |  |  |  |  |  |  |  | 30 |  |  |
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger |  |  |  |  |  |  |  | 130.00% |  |  |
Maximum [Member] | Société Générale S.A. [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Option to Extend, Debt Instrument Term |  |  |  |  |  |  |  | 5 years |  |  |
Maximum [Member] | Revolving Credit Facility [Member] | JPMorgan Chase Bank, N.A. [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  |  |  |  | $ 25,000,000.0 |  |  | $ 25,000,000.0 |  |  |
Convertible Debt | Convertible Note due 2022 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fair value of Convertible Senior Notes due 2022 used to settle Convertible Senior Notes due 2020 |  |  |  |  |  | 44,400,000 |  |  |  |  |
Extinguishment of Debt, Amount |  | 44,400,000 |  |  |  |  |  |  |  |  |
Convertible Debt | Convertible Note due 2020 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Principal amount |  | 8,100,000 |  |  |  | $ 8,100,000 |  |  |  |  |
Loss on debt extinguishment |  |  |  |  |  |  | 5,700,000 |  | $ 5,700,000 |  |
Convertible Debt | Long-term Debt [Member] | Convertible Note due 2020 | Privately Negotiated Transactions [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Extinguishment of Debt, Amount |  |  |  |  |  |  | 82,500,000 |  |  |  |
Convertible Debt | Additional Paid-in Capital [Member] | Convertible Note due 2020 | Privately Negotiated Transactions [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Extinguishment of Debt, Amount |  |  |  |  |  |  | $ 27,100,000 |  |  |  |
Liability Component Immediately Prior To Extinguishment [Member] | Convertible Note due 2020 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Extinguishment of Debt, Amount |  | 37,400,000 |  |  |  |  |  |  |  |  |
Equity Component Allocated to Additional Paid-in Capital [Member] | Additional Paid-in Capital [Member] | Convertible Note due 2020 |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Extinguishment of Debt, Amount |  | $ 7,000,000.0 |  |  |  |  |  |  |  |  |
Euribor Future [Member] | Loans Backed By French Research And Development Tax Credit Receivables [Member] | TVN [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Adjusted LIBOR or EURIBOR Rate, Term |  |  |  |  |  |  |  | 1 month |  |  |
One Month LIBOR [Member] | Revolving Credit Facility [Member] | JPMorgan Chase Bank, N.A. [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Adjusted LIBOR or EURIBOR Rate, Term |  |  |  |  |  |  |  | 1 month |  |  |
London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member] | JPMorgan Chase Bank, N.A. [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Basis Spread on Variable Rate |  |  |  |  |  |  |  | 2.50% |  |  |
LIBOR for interest period of one, two or three months [Member] | Revolving Credit Facility [Member] | JPMorgan Chase Bank, N.A. [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Basis Spread on Variable Rate |  |  |  |  |  |  |  | 2.25% |  |  |
Two Month LIBOR [Member] | Revolving Credit Facility [Member] | JPMorgan Chase Bank, N.A. [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Adjusted LIBOR or EURIBOR Rate, Term |  |  |  |  |  |  |  | 2 months |  |  |
Three Month LIBOR [Member] | Revolving Credit Facility [Member] | JPMorgan Chase Bank, N.A. [Member] |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Adjusted LIBOR or EURIBOR Rate, Term |  |  |  |  |  |  |  | 3 months |  |  |
[1] | As of September 25, 2020 and December 31, 2019, loans backed by French R&D tax credit receivables were $13.0 million and $15.1 million, respectively. As of September 25, 2020, the French Subsidiary had an aggregate of $19.5 million of R&D tax credit receivables from the French government from 2021 through 2024. See Note 8, “Balance Sheet Components” for additional information. These tax loans have a fixed rate of 0.6%, plus EURIBOR 1 month + 1.3% and mature between 2021 through 2023. The remaining loans of $1.5 million at September 25, 2020, primarily relate to financial support from French government agencies for R&D innovation projects at minimal interest rates, and these loans mature between 2020 through 2025.
[2] | Refer to the below section “Relief Loans” for the description of these loans.

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