Business Acquisition, Pro Forma Earnings Per Share [Abstract]

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The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Acquisitions - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 28, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues											$ 565,710
Net Income Attributable to Kadant											$ 44,159
Earnings per Share Attributable to Kadant:
Basic (in dollars per share)											$ 4.02
Diluted (in dollars per share)											$ 3.90
Net Income Attributable to Kadant	$ 8,749	$ 16,115	$ 16,304	$ 10,900	$ 18,422	$ 18,784	$ 12,349	$ 10,858	$ 52,068	$ 60,413	$ 31,092
Syntron Material Handling Group, LLC
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues									704,644	719,142
Net Income Attributable to Kadant									$ 56,409	$ 56,511
Earnings per Share Attributable to Kadant:
Basic (in dollars per share)									$ 5.02	$ 5.10
Diluted (in dollars per share)									$ 4.92	$ 4.96
Syntron Material Handling Group, LLC \| Acquisition-related transaction costs
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant									$ 843	$ (843)
Syntron Material Handling Group, LLC \| Inventory revalued
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant									3,549	(3,549)
Syntron Material Handling Group, LLC \| Intangible amortization related to acquired backlog
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant									$ 1,323	$ (1,323)
NII FPG And Unaflex, LLC Acquisitions \| Acquisition-related transaction costs
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant											5,360
NII FPG And Unaflex, LLC Acquisitions \| Inventory revalued
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant											5,137
NII FPG And Unaflex, LLC Acquisitions \| Intangible amortization related to acquired backlog
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant											1,438
NII FPG And Unaflex, LLC Acquisitions \| Income related to gain on sale of building
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant											$ 852