Earnings Per Share (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
Numerator for basic and diluted EPS:
Net income	$ (20,828)	$ 19,966	$ 11,144	$ 10,564	$ (8,232)	$ 9,320	$ 7,313	$ 3,050	$ 20,846	$ 11,451	$ 25,740
Denominator for basic EPS:
Weighted-average shares outstanding									20,212	20,027	19,983
Effect of dilutive securities:
Diluted potential common shares (in shares)									401	388	230
Denominator for diluted EPS:
Adjusted weighted-average shares outstanding									20,613	20,415	20,213
Basic EPS (in usd per share)	$ (1.03)	$ 0.99	$ 0.55	$ 0.52	$ (0.41)	$ 0.47	$ 0.37	$ 0.15	$ 1.03	$ 0.57	$ 1.29
Diluted EPS (in usd per share)	$ (1.03)	$ 0.97	$ 0.54	$ 0.51	$ (0.41)	$ 0.46	$ 0.36	$ 0.15	$ 1.01	$ 0.56	$ 1.27
Stock Appreciation Rights (SARs)
Effect of dilutive securities:
Dilutive effect of share-based compensation (in shares)									170	174	74
Restricted Stock Units (RSUs)
Effect of dilutive securities:
Dilutive effect of share-based compensation (in shares)									85	96	88
Performance-Based Restricted Stock Units
Effect of dilutive securities:
Dilutive effect of share-based compensation (in shares)									146	118	68