Earnings per Share - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 28, 2020	Mar. 30, 2019
Net Income Attributable to Kadant:
Net Income Attributable to Kadant	$ 12,531	$ 10,900
Basic Weighted Average Shares (in shares)	11,432	11,133
Effect of Stock Options, Restricted Stock Units and Employee Stock Purchase Plan Shares (in shares)	76	252
Diluted Weighted Average Shares (in shares)	11,508	11,385
Basic Earnings per Share (in dollars per share)	$ 1.10	$ 0.98
Diluted Earnings per Share (in dollars per share)	$ 1.09	$ 0.96