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. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Amounts Attributable to Kadant:
Net Income	$ 18,784	$ 13,285	$ 41,991	$ 30,332
Basic Weighted Average Shares (in shares)	11,101	11,004	11,078	10,986
Effect of Stock Options, Restricted Stock Units and Employee Stock Purchase Plan Shares (in shares)	320	340	310	296
Diluted Weighted Average Shares (in shares)	11,421	11,344	11,388	11,282
Basic Earnings per Share (in dollars per share)	$ 1.69	$ 1.21	$ 3.79	$ 2.76
Diluted Earnings per Share (in dollars per share)	$ 1.64	$ 1.17	$ 3.69	$ 2.69