Summary of Significant Accounting Policies - Service Maintenance Agreements (Details)	9 Months Ended
Sep. 30, 2019
Summary of Significant Accounting Policies
The term of the renewable service maintenance agreements (in years)	1 year

The term of renewable service maintenance agreements in years.

No definition available.

Name:	fix_RenewableServiceMaintenanceAgreementsTerm
Namespace Prefix:	fix_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration