Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 29, 2019 USD ($) Customer	Jun. 30, 2018 Customer	Jun. 29, 2019 USD ($) Customer	Jun. 30, 2018 USD ($)	Dec. 29, 2018 Customer	Dec. 30, 2018 USD ($)
Disclosure Summary Of Significant Accounting Policies [Line Items]
Extended product warranty period			1 year
Extended warranty, period to determine nature of sale			60 days
Deferred revenue recognized			$ 800	$ 900
Products warranty period			2 years
Right-of-use assets	$ 3,390		$ 3,390			$ 4,000
Lease liabilities	$ 3,879		$ 3,879			4,500
Deferred rent related to operating lease						$ 500
Revenue, Total | Customer Concentration Risk
Disclosure Summary Of Significant Accounting Policies [Line Items]
Number of customers | Customer	0	0	0
Accounts Receivable | Credit Concentration Risk
Disclosure Summary Of Significant Accounting Policies [Line Items]
Number of customers | Customer			0		0
Royalty Agreements
Disclosure Summary Of Significant Accounting Policies [Line Items]
Number of customers | Customer			2
IQ 532/577 Laser Consoles
Disclosure Summary Of Significant Accounting Policies [Line Items]
Products warranty period			5 years