Earnings per Share - Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 28, 2019	Sep. 29, 2018	Sep. 28, 2019	Sep. 29, 2018
Amounts Attributable to Kadant:
Net Income Attributable to Kadant	$ 16,115	$ 18,784	$ 43,319	$ 41,991
Basic Weighted Average Shares (in shares)	11,267	11,101	11,198	11,078
Effect of Stock Options, Restricted Stock Units and Employee Stock Purchase Plan Shares (in shares)	202	320	236	310
Diluted Weighted Average Shares (in shares)	11,469	11,421	11,434	11,388
Basic Earnings per Share (in dollars per share)	$ 1.43	$ 1.69	$ 3.87	$ 3.79
Diluted Earnings per Share (in dollars per share)	$ 1.41	$ 1.64	$ 3.79	$ 3.69