Earnings Per Share - Additional Information (Detail) - shares	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Line Items]
Class B common stock conversion, number of shares	2,602,528	2,709,194

Class B common stock securities that may be converted to Common stock securities at any time on a one-for-one basis at the option of the shareholder.

No definition available.

Name:	wso_ConvertibleClassBCommonStockOutstanding
Namespace Prefix:	wso_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant