Note 13 - Retirement Benefit Plans - Reconciliation of Level 3 Investments (Details) - Pension Plan [Member] - Foreign Plan [Member] - UK Pension Plan [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Fair value at beginning of year	$ 13.3	$ 12.2
Purchases, sales, issuances and settlements, net	0.2	0.1
Net (loss) gain	(0.4)	0.6
Foreign currency	(0.2)	0.4
Fair value at end of year	$ 12.9	$ 13.3

Amount of increase (decrease) in asset measured at fair value on recurring basis using unobservable input (level 3) due to foreign currency effects.

No definition available.

+ Details

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Namespace Prefix:	tnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss) recognized from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

No definition available.

+ Details

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Namespace Prefix:	tnc_
Data Type:	xbrli:monetaryItemType
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- Definition

Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

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Balance Type:	debit
Period Type:	duration

- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

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- Details

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Namespace Prefix:
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Period Type:

- Details

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