Convertible Notes, Other Debts And Capital Leases - Additional Information (Detail) $ / shares in Units, shares in Millions			3 Months Ended	6 Months Ended	12 Months Ended
		Dec. 14, 2015 shares	Jun. 29, 2018 USD ($) $ / shares	Jun. 29, 2018 USD ($) $ / shares	Dec. 31, 2015 USD ($) day $ / shares	Dec. 31, 2017 USD ($)	Jun. 30, 2017 $ / shares
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					4.00%
Debt Instrument, Face Amount			$ 128,250,000	$ 128,250,000	$ 128,250,000	$ 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	$ 5.75		$ 5.75
Debt Issuance Cost, Gross, Noncurrent					$ 4,100,000
Percentage Of Principal Amount Of Convertible Notes Is Equal To Repurchase Price					100.00%
Term loans			$ 1,081,000	$ 1,081,000		1,282,000
Financing from French government agencies related to various government incentive programs (1)	[1]		14,401,000	14,401,000		20,565,000
Carrying amount of equity component			26,062,000	26,062,000		26,062,000
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%
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%
Privately Negotiated Transactions [Member]
Debt Instrument [Line Items]
Proceeds from Convertible Debt					$ 49,900,000
Stock Repurchased and Retired During Period, Shares | shares		11.1
TVN [Member]
Debt Instrument [Line Items]
Proceeds from Convertible Debt					$ 74,200,000
Income Taxes Receivable			$ 24,000,000	$ 24,000,000
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%
Adjusted EURIBOR Rate, Term			1 month
Debt Instrument, Basis Spread on Variable Rate			1.30%
Financing from French government agencies related to various government incentive programs (1)	[1]		$ 12,000,000	$ 12,000,000		$ 17,700,000
Loans From French Government For R&D Innovation Projects [Member]
Debt Instrument [Line Items]
Financing from French government agencies related to various government incentive programs (1)	[1]		2,400,000	2,400,000
Revolving Credit Facility [Member] | Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity			15,000,000	15,000,000
Minimum Net Worth Required for Compliance			20,000,000	20,000,000
Line of Credit Facility, Fair Value of Amount Outstanding			$ 0	$ 0
Outstanding Borrowing Limit Based on Eligible Receivables, Percentage			85.00%	85.00%
Covenant Ratio of Short Term Asset to Short Term Liabilities			110.00%	110.00%
Minimum Liquidity Amount			$ 10,000,000	$ 10,000,000
Letters of Credit Outstanding, Amount			$ 2,400,000	$ 2,400,000
London Interbank Offered Rate (LIBOR) [Member] | Revolving Credit Facility [Member] | Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				2.25%
Not Comply with Liquidity Requirement [Member] | Prime Rate [Member] | Revolving Credit Facility [Member] | Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				0.25%

[1] As of June 29, 2018 and December 31, 2017, loans backed by French R&D tax credit receivables were $12.0 million and $17.7 million, respectively. As of June 29, 2018, the TVN French Subsidiary had an aggregate of $24.0 million of R&D tax credit receivables from the French government from 2018 through 2022. See Note 6, “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 2018 through 2020. The remaining loans of $2.4 million at June 29, 2018, primarily relate to financial support from French government agencies for R&D innovation projects at minimal interest rates, and these loans mature between 2018 through 2025.