Summary of Significant Accounting Policies - Basic and Diluted Earning (Loss) Per Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 31, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income (loss)	$ (5,259)	$ 1,088	$ 940	$ 414	$ (419)	$ 40	$ 434	$ 751	$ (2,817)	$ 806	$ (34,638)
Weighted average number of shares outstanding, basic (in shares)									13,805	15,055	15,593
Basic (in dollars per share)	$ (0.39)	$ 0.09	$ 0.07	$ 0.03	$ (0.03)	$ 0.00	$ 0.03	$ 0.05	$ (0.20)	$ 0.05	$ (2.22)
Number of shares, attributable to equity based compensation plans (in shares)										269
Weighted average number of shares outstanding, diluted (in shares)									13,805	15,324	15,593
Diluted (in dollars per share)	$ (0.39)	$ 0.09	$ 0.07	$ 0.03	$ (0.03)	$ 0.00	$ 0.03	$ 0.05	$ (0.20)	$ 0.05	$ (2.22)