Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 28, 2018
Statement Of Financial Position [Abstract]
Accounts receivable, net of allowance for contract losses and doubtful accounts	$ 5,218	$ 4,066
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	65,707,000	65,707,000
Treasury stock, shares	13,682,000	14,208,000