Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jul. 01, 2016	Apr. 01, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator for basic and diluted EPS:
Net income	$ (8,232)	$ 9,320	$ 7,313	$ 3,050	$ 6,778	$ 8,045	$ 5,549	$ 5,368	$ 11,451	$ 25,740	$ 32,158
Denominator for basic EPS:
Weighted-average shares outstanding									20,027	19,983	20,097
Effect of dilutive securities:
Diluted potential common shares (in shares)									388	230	305
Denominator for diluted EPS:
Adjusted weighted-average shares outstanding									20,415	20,213	20,402
Basic (in usd per share)	$ (0.41)	$ 0.47	$ 0.37	$ 0.15	$ 0.34	$ 0.40	$ 0.28	$ 0.27	$ 0.57	$ 1.29	$ 1.60
Diluted EPS (in usd per share)	$ (0.41)	$ 0.46	$ 0.36	$ 0.15	$ 0.33	$ 0.40	$ 0.27	$ 0.27	$ 0.56	$ 1.27	$ 1.58
Stock Appreciation Rights (SARs)
Effect of dilutive securities:
Dilutive effect of share-based compensation (in shares)									174	74	156
Restricted Stock Units (RSUs)
Effect of dilutive securities:
Dilutive effect of share-based compensation (in shares)									96	88	91
Performance Shares
Effect of dilutive securities:
Dilutive effect of share-based compensation (in shares)									118	68	58