UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 27, 2020	Dec. 31, 2019
Accounts receivable, allowance for credit losses	$ 509	$ 609
Preferred stock (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	50,000,000	50,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	500,000,000	500,000,000
Common stock, shares, issued (in shares)	79,026,508	75,785,952
Common stock, shares, outstanding (in shares)	79,026,508	75,785,952
U.S. treasuries
Short-term investments, amortized cost	$ 19,992	$ 19,967