Acquisitions - Acquired Intangible Assets (Details) $ in Thousands	Feb. 01, 2024 USD ($) Milestone
Summit Texas
Acquisitions
Estimated Fair Value	$ 170,100
Summit Texas \| Minimum \| Measurement Input, Inception Discount Rate
Acquisitions
Cash flow discount rate	18.50%
Summit Texas \| Maximum \| Measurement Input, Inception Discount Rate
Acquisitions
Cash flow discount rate	20.50%
Summit Texas \| Contingent earn-out obligations
Acquisitions
Number of earnings milestones \| Milestone	4
Term of earnings milestones	47 months
Estimated milestone payment, upper range	$ 20,500
Estimated milestone payment, lower range	$ 2,600
Summit Texas \| Contingent earn-out obligations \| Minimum \| Measurement Input, Inception Discount Rate
Acquisitions
Cash flow discount rate	18.20%
Summit Texas \| Contingent earn-out obligations \| Maximum \| Measurement Input, Inception Discount Rate
Acquisitions
Cash flow discount rate	19.50%
Summit Texas \| Backlog
Acquisitions
Estimated Useful Life	1 year 9 months 18 days
Estimated Fair Value	$ 35,800
Summit Texas \| Trade Name
Acquisitions
Estimated Useful Life	22 years 10 months 24 days
Estimated Fair Value	$ 11,300
Summit Texas \| Customer Relationships
Acquisitions
Estimated Useful Life	10 years
Estimated Fair Value	$ 123,000
J&S Utah
Acquisitions
Estimated Fair Value	$ 63,300
J&S Utah \| Minimum \| Measurement Input, Inception Discount Rate
Acquisitions
Cash flow discount rate	15.50%
J&S Utah \| Maximum \| Measurement Input, Inception Discount Rate
Acquisitions
Cash flow discount rate	17.00%
J&S Utah \| Contingent earn-out obligations
Acquisitions
Number of earnings milestones \| Milestone	3
Term of earnings milestones	35 months
Estimated milestone payment, upper range	$ 4,700
Estimated milestone payment, lower range	$ 1,100
J&S Utah \| Contingent earn-out obligations \| Minimum \| Measurement Input, Inception Discount Rate
Acquisitions
Cash flow discount rate	15.40%
J&S Utah \| Contingent earn-out obligations \| Maximum \| Measurement Input, Inception Discount Rate
Acquisitions
Cash flow discount rate	16.50%
J&S Utah \| Backlog
Acquisitions
Estimated Useful Life	1 year 9 months 18 days
Estimated Fair Value	$ 12,900
J&S Utah \| Trade Name
Acquisitions
Estimated Useful Life	22 years
Estimated Fair Value	$ 10,600
J&S Utah \| Customer Relationships
Acquisitions
Estimated Useful Life	9 years
Estimated Fair Value	$ 39,800

The number of earnings milestone.

No definition available.

Name:	fix_BusinessCombinationNumberOfEarningsMilestones
Namespace Prefix:	fix_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The term of earnings milestones.

+ References

No definition available.

+ Details

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

- Definition

Amount of probable cash flows discount rate.

+ References

No definition available.

+ Details

Name:	fix_CashFlowDiscountRate
Namespace Prefix:	fix_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482665/350-30-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482665/350-30-50-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482665/350-30-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482665/350-30-50-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 985
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481283/985-20-50-2

+ Details

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

- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482665/350-30-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 985
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481283/985-20-50-2

+ Details

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

For contingent consideration arrangements recognized in connection with a business combination, this element represents an estimate of the high-end of the potential range (undiscounted) of the consideration which may be paid.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479581/805-30-50-1

+ Details

Name:	us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For contingent consideration arrangements and indemnification assets recognized in connection with a business combination, this element represents an estimate of the low-end of the potential range (undiscounted) of the consideration which may be paid.

+ References

+ Details

Name:	us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of identifiable intangible assets recognized as of the acquisition date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 55
-Paragraph 37
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479303/805-10-55-37

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479907/805-20-50-1

+ Details

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=fix_SummitIndustrialConstructionLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputInceptionDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=fix_ContingentConsiderationObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_OrderOrProductionBacklogMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TradeNamesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CustomerRelationshipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=fix_JSMechanicalContractorsIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: