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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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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.

+ References

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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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-Publisher FASB
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Acquisitions - Pro Forma Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Oct. 01, 2016	Jul. 02, 2016	Apr. 02, 2016	Dec. 30, 2017	Dec. 31, 2016	Jan. 02, 2016
Earnings per Share Attributable to Kadant:
Nonrecurring adjustments	$ 760	$ 13,285	$ 8,096	$ 8,951	$ 7,733	$ 9,157	$ 8,311	$ 6,876	$ 31,092	$ 32,077	$ 34,389
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:
Nonrecurring adjustments									$ 5,360	$ (5,360)
NII FPG and Unaflex, LLC \| Inventory revalued
Earnings per Share Attributable to Kadant:
Nonrecurring adjustments									5,137	(5,137)
NII FPG and Unaflex, LLC \| Intangible amortization related to acquired backlog
Earnings per Share Attributable to Kadant:
Nonrecurring adjustments									1,438	(1,669)
NII FPG and Unaflex, LLC \| Gain on sale of building
Earnings per Share Attributable to Kadant:
Nonrecurring adjustments									$ (852)
PAAL
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues										427,273	444,350
Net Income Attributable to Kadant										$ 35,321	$ 33,881
Earnings per Share Attributable to Kadant:
Basic (in dollars per share)										$ 3.25	$ 3.12
Diluted (in dollars per share)										$ 3.17	$ 3.05
PAAL \| Acquisition-related transaction costs
Earnings per Share Attributable to Kadant:
Nonrecurring adjustments										$ 1,832	$ (1,832)
PAAL \| Inventory revalued
Earnings per Share Attributable to Kadant:
Nonrecurring adjustments										458	(458)
PAAL \| Intangible amortization related to acquired backlog
Earnings per Share Attributable to Kadant:
Nonrecurring adjustments										1,468	(1,468)
PAAL \| Pre-acquisition debt
Earnings per Share Attributable to Kadant:
Nonrecurring adjustments										$ 454	$ 1,636