Employee Benefit Plans (Details) $ in Millions	12 Months Ended
Dec. 31, 2024 USD ($) employee	Dec. 31, 2023 USD ($) employee	Dec. 31, 2022 USD ($)
Employee Benefit Plans
Percentage of contributions of covered employees' salaries or wages	2.50%
Contribution	$ 35.3	$ 22.9	$ 19.8
Number of employees who are union members \| employee	50	7
Contributions made to multi-employer pension plans	$ 0.0	$ 0.0	$ 0.0
Combined face value of life insurance policies	101.9	87.8
Cash surrender value	$ 9.0	$ 7.5

Represents the face amount of life insurance policies taken by the entity for their employees.

No definition available.

Name:	fix_LifeInsuranceContractsFaceAmount
Namespace Prefix:	fix_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of amounts which could be received based on the terms of the insurance contract upon surrendering life policies owned by the entity.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(17))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

+ Details

Name:	us-gaap_CashSurrenderValueOfLifeInsurance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480794/715-70-50-1

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of entity's employees covered by multiemployer plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 80
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480576/715-80-50-6

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 80
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480576/715-80-50-11

+ Details

Name:	us-gaap_MultiemployerPlanNumberOfEmployeesCovered
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of contribution received by multiemployer pension plan from all employers participating in multiemployer pension plan determined to be individually insignificant.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 80
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480576/715-80-50-7

+ Details

Name:	us-gaap_MultiemployerPlanPensionInsignificantPlanContribution
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration