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. 29, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant	$ 18,422	$ 18,784	$ 12,349	$ 10,858	$ 760	$ 13,285	$ 8,096	$ 8,951	$ 60,413	$ 31,092	$ 32,077
NII FPG and Unaflex, LLC
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues										565,710	508,832
Net Income Attributable to Kadant										$ 44,159	$ 30,638
Earnings per Share Attributable to Kadant:
Basic (in dollars per share)										$ 4.02	$ 2.82
Diluted (in dollars per share)										$ 3.90	$ 2.75
NII FPG and Unaflex, LLC \| Acquisition-related transaction costs
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant										$ 5,360	$ (5,360)
NII FPG and Unaflex, LLC \| Inventory revalued
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant										5,137	(5,137)
NII FPG and Unaflex, LLC \| Intangible amortization related to acquired backlog
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant										1,438	$ (1,669)
NII FPG and Unaflex, LLC \| Income related to gain on sale of building
Earnings per Share Attributable to Kadant:
Net Income Attributable to Kadant										$ (852)