Summary of Significant Accounting Policies - Weighted Average Number of Shares Outstanding Used to Compute Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Accounting Policies [Abstract]
Net income	$ 6,501	$ 8,303	$ 19,521	$ 23,590
Weighted-average number of common shares outstanding
Basic weighted-average common shares outstanding (in shares)	11,703	11,551	11,660	11,501
Dilutive potential common shares (in shares)	256	243	226	283
Diluted weighted-average common shares outstanding (in shares)	11,959	11,794	11,886	11,784
Earnings per share
Basic (in dollars per share)	$ 0.56	$ 0.72	$ 1.67	$ 2.05
Diluted (in dollars per share)	$ 0.54	$ 0.70	$ 1.64	$ 2.00