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Basis of Presentation - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) Entity
Significant Accounting Policies [Line Items]
Number of joint ventures | Entity	3
Cumulative-effect adjustment to retained earnings | $	$ 301

X

- Definition

Amount of the cumulative effect on retained earnings net of related income tax effect.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	duration

X

- Definition

Number of joint ventures. Joint ventures are entities operated by the controlling interest for the mutual benefit of the members.

+ References

No definition available.

+ Details

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Namespace Prefix:	wso_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Significant Accounting Policies [Line Items]

+ References

No definition available.

+ Details

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Namespace Prefix:	wso_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration