Entity Listings [Table] Entity Listings [Table] Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] 4.0433% Interest Rate Swap, Maturing September 15, 2025 to December 31, 2026 4.0433% Interest Rate Swap, Maturing September 15, 2025 to December 31, 2026 [Member] 4.0433% Interest Rate Swap, Maturing September 15, 2025 to December 31, 2026 Statistical Measurement [Domain] Statistical Measurement [Domain] Property and equipment Business Combination, Recognized Asset Acquired, Property, Plant, and Equipment Award Timing Predetermined Award Timing Predetermined [Flag] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] Entity File Number Entity File Number Additional Paid-in Capital Additional Paid-in Capital [Member] Interest rate swap 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and Related Balance Sheet Accounts Revenue from Contract with Customer [Text Block] Accounts payable Increase (Decrease) in Accounts Payable, Trade 3.4396% Interest Rate Swap, Maturing at December 2026 3.4396% Interest Rate Swap, Maturing at December 2026 [Member] 3.4396% Interest Rate Swap, Maturing at December 2026 Debt instrument, covenant, minimum availability milestone of facility size (as percent) Debt Instrument, Threshold To Test Net Leverage Ratio, Outstanding Borrowings Compared To Facility Size, Percent, Minimum Debt Instrument, Threshold To Test Net Leverage Ratio, Outstanding Borrowings Compared To Facility Size, Percent, Minimum Other comprehensive income (loss) Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Schedule of Segment Reporting Information Schedule of Segment Reporting Information, by Segment [Table Text Block] Revenue, remaining performance obligation Revenue, Remaining Performance Obligation, Amount Adjustment to Compensation, 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Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Purchase price receivable Business Combination, Consideration Transferred, Purchase Price Receivable (Payable) Business Combination, Consideration Transferred, Purchase Price Receivable (Payable) Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Total Legence stockholders' equity Equity, Attributable to Parent Other comprehensive income (loss), net: Other Comprehensive Income (Loss), Net of Tax [Abstract] Insider Trading Policies and Procedures [Line Items] Compensation expense (benefit) Share-Based Payment Arrangement, Expense Common stock, shares authorized (in shares) Common Stock, Shares Authorized Hedging Designation [Domain] Hedging Designation [Domain] Goodwill and Intangible Assets Disclosure [Abstract] Current assets: Assets, Current [Abstract] Total liabilities and stockholders' equity Liabilities and Equity Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Interest rate (as percent) Line of Credit Facility, Interest Rate at Period End Issuance of Class A Common Stock for acquisitions (in shares) Stock Issued During Period, Shares, Acquisitions Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Jefferies Finance LLC Revolving Line Of Credit Jefferies Finance LLC Revolving Line Of Credit [Member] Jefferies Finance LLC Revolving Line Of Credit Cash and cash equivalents, beginning of period Cash and cash equivalents, end of period Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Including Discontinued Operation Liabilities and Equity Liabilities and Equity [Abstract] 3.2480% Interest Rate Swap, Maturing at December 2027 3.2480% Interest Rate Swap, Maturing at December 2027 [Member] 3.2480% Interest Rate Swap, Maturing at December 2027 Cover [Abstract] Cash equivalents - money market Cash and Cash Equivalents, Fair Value Disclosure Common unit, outstanding (in shares) Common unit, outstanding (in shares) Common Unit, Outstanding Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Maximum Maximum [Member] Equity Method Investment [Table] Equity Method Investment [Table] Net income attributable to noncontrolling interests Less: Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Sale of stock option period Sale Of Stock Option Period Sale Of Stock Option Period Accounting Policies [Abstract] Intangible assets, net Net Carrying Amount Finite-Lived Intangible Assets, Net Income Tax Contingency [Line Items] Income Tax Contingency [Line Items] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Term loan payments Repayments of Secured Debt Non-PEO NEO Average Total Compensation Amount Non-PEO NEO Average Total Compensation Amount Cash tax savings retained (as a percent) Tax Receivable Agreement, Cash Tax Savings Retained Tax Receivable Agreement, Cash Tax Savings Retained Debt Instrument [Line Items] Debt Instrument [Line Items] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Schedule of Share-Based Compensation Arrangements by Share-Based Payment Award [Table] Adjustment to Non-PEO NEO Compensation Footnote Adjustment to Non-PEO NEO Compensation Footnote [Text Block] Pay vs Performance Disclosure [Line Items] Forgone Recovery due to Disqualification of Tax Benefits, Amount Forgone Recovery due to Disqualification of Tax Benefits, Amount Acquisitions Business Combination [Text Block] Non-Rule 10b5-1 Arrangement Terminated Non-Rule 10b5-1 Arrangement Terminated [Flag] Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Income (loss) before income tax 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To Exercise Of Underwriters' Overallotment Option Incremental Common Shares Attributable To Dilutive Effect Of Exchange Of Stock Units Related To Exercise Of Underwriters' Overallotment Option Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Statement of Stockholders' Equity [Abstract] Schedule of Additional Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Variable Interest Entity [Table] Variable Interest Entity [Table] Statement of Cash Flows [Abstract] Company Selected Measure Amount Company Selected Measure Amount Cash Cash Comprehensive income attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Comprehensive income (loss) attributable to Legence Comprehensive Income (Loss), Net of Tax, Attributable to Parent Name Measure Name Letter of Credit Letter of Credit [Member] Schedule of Ownership of Legence Holdings Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table Text Block] Schedule of Compensation Expense And Corresponding Income Tax Benefit Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Term loan Secured Debt [Member] Current portion of operating lease liabilities (including $3,946 and $3,920 as of March 31, 2026 and December 31, 2025, respectively, from related parties) Operating Lease, Liability, Current Accrued and other current liabilities Accrued And Other Current Liabilities [Member] Accrued And Other Current Liabilities Deferred tax liabilities, net Deferred Income Tax Liabilities, Net Holdback Business Combination, Consideration Transferred, Liabilities Incurred, Holdback Business Combination, Consideration Transferred, Liabilities Incurred, Holdback Document Fiscal Period Focus Document Fiscal Period Focus Award Timing Method Award Timing Method [Text Block] Time Interests Time Interests [Member] Time Interests Award Type Award Type [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Income Tax Contingency [Table] Income Tax Contingency [Table] Legal Entity [Axis] Legal Entity [Axis] Schedule of Supplemental Pro Forma Information Business Combination, Pro Forma Information [Table Text Block] Total assets Total assets Assets 4.0433% Interest Rate Swap, Maturing at December 2026 4.0433% Interest Rate Swap, Maturing at December 2026 [Member] 4.0433% Interest Rate Swap, Maturing at December 2026 2027 Finite-Lived Intangible Asset, Expected Amortization, Year One Trading Symbol Trading Symbol Member's Equity Member Units [Member] Entity Address, City or Town Entity Address, City or Town Cash flows from operating activities: Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Weighted-average Remaining Life (in years) Acquired Finite-Lived Intangible Assets, Weighted Average Useful Life Concentration Risk Type [Axis] Concentration Risk Type [Axis] Non-PEO NEO Average Compensation Actually Paid Amount Non-PEO NEO Average Compensation Actually Paid Amount RSUs Restricted Stock Units (RSUs) [Member] Statement of Income Location, Balance [Domain] Statement of Income Location, Balance [Domain] Notes payable, noncurrent Notes Payable, Noncurrent Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Total consideration transferred Total consideration transferred Business Combination, Consideration Transferred Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] 2030 Finite-Lived Intangible Asset, Expected Amortization, Year Four Contract backlog Order or Production Backlog [Member] Entity Emerging Growth Company Entity Emerging Growth Company Current portion of tax receivable agreement liability - related party Tax Receivable Agreement Liability, Current Tax Receivable Agreement Liability, Current Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Asset Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Acquired Including Goodwill Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Acquired Including Goodwill Right-of-use assets obtained in exchange for new operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Revolver payments Revolver payments Repayments of Lines of Credit Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year Change in Fair Value as of Vesting Date of Prior Year Equity Awards Vested in Covered Year [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Compensation expense - Performance Interests Compensation Expense, Performance Interests Compensation Expense, Performance Interests Insider Trading Policies and Procedures Not Adopted Insider Trading Policies and Procedures Not Adopted [Text Block] Business Combination [Domain] Business Combination [Domain] Fees incurred from third parties Debt Instrument, Fee Amount Related Party Related Party [Member] Common stock, shares outstanding (in shares) Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Insurance Claims Insurance Claims [Member] Total 2025 Acquisitions Total 2025 Acquisitions [Member] Total 2025 Acquisitions PEO PEO [Member] Term loan borrowings (including $15,000 and $2,495 in 2026 and 2025, respectively, from related parties) Proceeds from Issuance of Secured Debt Schedule of Disaggregation of Revenue Disaggregation of Revenue [Table Text Block] LGN B Units LGN B Units [Member] LGN B Units Interest income Investment Income, Interest Valuation allowance, deferred tax asset, increase (decrease), amount Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount Changes in operating assets and liabilities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Installation & Maintenance Installation And Maintenance [Member] Installation And Maintenance Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Guarantor obligations, current carrying value Guarantor Obligations, Current Carrying Value Change in deferred tax assets valuation allowance, benefit Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount Schedule of Future Amortization of Intangible Assets Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Derivative Instruments and Hedging Activities Disclosure [Abstract] Accumulated Deficit Retained Earnings [Member] Prepaid expenses and other current assets Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Entity Address, Postal Zip Code Entity Address, Postal Zip Code Restatement Determination Date Restatement Determination Date Share-Based Payment Arrangement [Abstract] Income Statement [Abstract] Interest rate swap instruments Derivative Asset Income tax (benefit) expense Income Tax Expense (Benefit) Debt instrument, basis spread on variable rate (as percent) Debt Instrument, Basis Spread on Variable Rate Common Class B Class B common stock Common Class B [Member] Sale of Stock [Domain] Sale of Stock [Domain] Document Information [Line Items] Document Information [Line Items] Preferred stock, shares issued (in shares) Preferred Stock, Shares Issued Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Product and Service [Domain] Product and Service [Domain] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Customer 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[Member] Schedule of Asset and Liabilities Business Combination, Recognized Asset Acquired and Liability Assumed [Table Text Block] Operating lease right-of-use asset lease expense Operating Lease, Right-of-Use Asset, Periodic Reduction Compensation Actually Paid vs. Company Selected Measure Compensation Actually Paid vs. Company Selected Measure [Text Block] Acquisitions Goodwill, Acquired During Period City Area Code City Area Code Consideration paid for acquisitions, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Award Timing, How MNPI Considered Award Timing, How MNPI Considered [Text Block] All Trading Arrangements All Trading Arrangements [Member] Equity Awards Adjustments, Footnote Equity Awards Adjustments, Footnote [Text Block] Total Shareholder Return Vs Peer Group Total Shareholder Return Vs Peer Group [Text Block] Accrued and other current liabilities Accrued and other current liabilities Accrued Liabilities, Current Commitments and Contingencies Disclosure [Abstract] Cash flows from investing activities: Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Legence Corp Legence Corp [Member] Legence Corp Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation 3.4581% Interest Rate Swap, Maturing at December 2028 3.4581% Interest Rate Swap, Maturing at December 2028 [Member] 3.4581% Interest Rate Swap, Maturing at December 2028 Debt instrument, term (in years) Debt Instrument, Term Related Party Transactions [Abstract] Equity Method Investments and Joint Ventures [Abstract] Performance Interests Performance Interests [Member] Performance Interests Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Subsequent Event Subsequent Event [Member] Cost of revenue Cost of Sales [Member] Cash Flow Hedging Cash Flow Hedging [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Goodwill Goodwill, Beginning Balance Goodwill, Ending Balance Goodwill Equity Valuation Assumption Difference, Footnote Equity Valuation Assumption Difference, Footnote [Text Block] PEO Total Compensation Amount PEO Total Compensation Amount Long-Term Debt, Type [Axis] Long-Term Debt, Type [Axis] Prepaid expenses and other current assets Prepaid Expenses and Other Current Assets [Member] Money Market Funds Money Market Funds [Member] Operating lease right-of-use assets Business Combination, Recognized Asset Acquired, Asset, Operating Lease Right-of-use Assets Business Combination, Recognized Asset Acquired, Asset, Operating Lease Right-of-use Assets 2026 (nine months remaining) Finite-Lived Intangible Asset, Expected Amortization, Remainder of Fiscal Year Denominator—basic: Weighted Average Number of Shares Outstanding, Basic [Abstract] Contribution from Legence Parent II for Series A Interests Contributions From Parent II For Series A Interests Contributions From Parent II For Series A Interests Numerator—diluted: Net Income (Loss) Available to Common Stockholders, Diluted [Abstract] Equity Components [Axis] Equity Components [Axis] Non-Rule 10b5-1 Arrangement Adopted Non-Rule 10b5-1 Arrangement Adopted [Flag] Number of reportable segments Number of Reportable Segments Accumulated Gain (Loss), Net, Cash Flow Hedge, Noncontrolling Interest Accumulated Gain (Loss), Net, Cash Flow Hedge, Noncontrolling Interest [Member] Deferred consideration related to Bowers acquisition Deferred Consideration Related To Acquisition [Member] Deferred Consideration Related To Acquisition Accounts receivable Business Combination, Recognized Asset Acquired, Receivable, Current Accumulated goodwill impairment Goodwill, Impaired, Accumulated Impairment Loss Other Performance Measure, Amount Other Performance Measure, Amount Debt issuance costs Payments of Debt Issuance Costs Entity Address, State or Province Entity Address, State or Province Finance lease payments Finance Lease, Principal Payments Antidilutive Security, Excluded EPS Calculation [Table] Antidilutive Security, Excluded EPS Calculation [Table] Related and Nonrelated Parties [Domain] Related and Nonrelated Parties [Domain] Total current liabilities Liabilities, Current Over-Allotment Option Over-Allotment Option [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Individual: Individual [Axis] Promissory Note Payable In Connection With 2023 Acquisition Promissory Note Payable In Connection With 2023 Acquisition [Member] Promissory Note Payable In Connection With 2023 Acquisition Right-of-use assets obtained in exchange for new finance lease liabilities Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Entity [Domain] Entity [Domain] Cash used in investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Revenue, performance obligation expected timing of satisfaction period Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table Aggregate Change in Present Value of Accumulated Benefit for All Pension Plans Reported in Summary Compensation Table [Member] Interest paid, net of interest rate swaps Interest Paid, Excluding Capitalized Interest, Operating Activity Document Fiscal Year Focus Document Fiscal Year Focus Installation & Fabrication Installation And Fabrication [Member] Installation And Fabrication Effect of assumed exchange of LGN B Units prior to exercise of underwriters' overallotment option Dilutive Securities, Effect on Basic Earnings Per Share, Underwriters' Overallottment Dilutive Securities, Effect on Basic Earnings Per Share, Underwriters' Overallottment Operating lease right-of-use assets (including $19,082 and $20,025 as of March 31, 2026 and December 31, 2025, respectively, from related parties) Operating Lease, Right-of-Use Asset Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Legacy Owners ownership of Legence Holdings Common Units (as percent) Subsidiary, Ownership Percentage, Noncontrolling Owner Effective income tax rate (as percent) Effective Income Tax Rate Reconciliation, Percent Entity Interactive Data Current Entity Interactive Data Current Carrying Value Reported Value Measurement [Member] Acquisition-related costs Business Combination, Acquisition-Related Cost, Expense Expected life (years) Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Operating lease liabilities, net of current portion Business Combination, Recognized Liability Assumed, Operating Lease Liabilities, Noncurrent Business Combination, Recognized Liability Assumed, Operating Lease Liabilities, Noncurrent Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Engineering & Consulting Engineering And Consulting [Member] Engineering And Consulting Equity [Abstract] Derivatives Derivatives, Policy [Policy Text Block] Segment Information Segment Reporting Disclosure [Text Block] Principal payments on term loans Debt Instrument, Periodic Payment, Principal Goodwill [Table] Goodwill [Table] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Current portion of long-term debt Less: Current portion Long-Term Debt and Lease Obligation, Current Issuance of Class A Common Stock for acquisitions Stock Issued During Period, Shares, Acquisitions, Percent Stock Issued During Period, Shares, Acquisitions, Percent Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' 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Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount Revolving Credit Facility Revolving Credit Facility [Member] Finance lease liabilities Finance Lease, Liability Arrangement Duration Trading Arrangement Duration Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Acquiree's earnings (loss) since acquisition date Business Combination, Acquiree's Earnings (Loss) since Acquisition Date, Actual Contract liabilities Contract with Customer, Liability, Current Segments [Axis] Segments [Axis] Schedule of Derivative Assets and Derivative Liabilities Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Prepaid expenses and other current assets Increase (Decrease) in Prepaid Expense and Other Assets Exercise Price Award Exercise Price Entity Filer Category Entity Filer Category Local Phone Number Local Phone Number Class of Stock [Domain] Class of Stock [Domain] Additional 402(v) Disclosure Additional 402(v) Disclosure [Text Block] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Stock-Based Compensation and Long-term Incentive Awards Share-Based Payment Arrangement [Text Block] Engineering & Design Engineering And Design [Member] Engineering And Design Cash Business Combination, Recognized Asset Acquired, Cash and Cash Equivalent Assets Assets [Abstract] Credit Facility [Axis] Credit Facility [Axis] Maximum annual cash payments Share-based Compensation Arrangement By Share-based Payment Award, Maximum Purchase Value During Offering Period, Per Employee Share-based Compensation Arrangement By Share-based Payment Award, Maximum Purchase Value During Offering Period, Per Employee Promissory Note Payable In Connection With 2024 And 2022 Acquisition Promissory Note Payable In Connection With 2024 And 2022 Acquisition [Member] Promissory Note Payable In Connection With 2024 And 2022 Acquisition Underlying Security Market Price Change Underlying Security Market Price Change, Percent 2029 Finite-Lived Intangible Asset, Expected Amortization, Year Three Statement of Financial Position Location, Balance [Axis] Statement of Financial Position Location, Balance [Axis] Debt Instrument [Axis] Debt Instrument [Axis] Fair Value Measurements Fair Value Disclosures [Text Block] Business Combination [Line Items] Business Combination [Line Items] Credit Facility [Domain] Credit Facility [Domain] Gross Carrying Amount Finite-Lived Intangible Assets, Gross Stockholders' equity Equity, Attributable to Parent [Abstract] Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Self Insurance Reserve, Current Self Insurance Reserve, Current Business Combination, Pro Forma Information, Nonrecurring Adjustment [Axis] Business Combination, Pro Forma Information, Nonrecurring Adjustment [Axis] Entity Address, Address Line One Entity Address, Address Line One Accumulated Other Comprehensive Income AOCI Attributable to Parent [Member] Stated interest rate (as percent) Debt Instrument, Interest Rate, Stated Percentage Accrued and other current liabilities Increase (Decrease) in Accrued Liabilities and Other Operating Liabilities Operating lease liabilities, net of current portion (including $16,290 and $17,282 as of March 31, 2026 and December 31, 2025, respectively, from related parties) Operating Lease, Liability, Noncurrent Exchange of Class B Common Stock to Class A Common Stock (in shares) Effects of exercise of underwriters' overallotment option (in shares) Stock Issued During Period, Shares, Conversion of Convertible Securities Business Combination, Asset Acquisition, Transaction between Entities under Common Control, and Joint Venture Formation [Abstract] Metrix Metrix Engineers, LLC [Member] Metrix Engineers, LLC Ownership [Axis] Ownership [Axis] Business Combination, Pro Forma Information, Nonrecurring Adjustment [Domain] Business Combination, Pro Forma Information, Nonrecurring Adjustment [Domain] Derivatives Derivative Instruments and Hedging Activities Disclosure [Text Block] Fair Value as of Grant Date Award Grant Date Fair Value Entity Registrant Name Entity Registrant Name Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] Secondary Offering Secondary Offering [Member] Secondary Offering Contract assets Business Combination, Recognized Asset Acquired, Contract Assets Business Combination, Recognized Asset Acquired, Contract Assets Derivative Instruments and Hedging Activities Disclosures [Table] Derivative Instruments and Hedging Activities Disclosures [Table] Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Depreciation of property and equipment Depreciation, Nonproduction Unrecognized compensation expense Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Effect of assumed exchange of LGN B Units Dilutive Securities, Effect on Basic Earnings Per Share, Dilutive Convertible Securities Document Quarterly Report Document Quarterly Report Changed Peer Group, Footnote Changed Peer Group, Footnote [Text Block] Counterparty Name [Domain] Counterparty Name [Domain] Other 2025 Acquisition Other 2025 Acquisition [Member] Other 2025 Acquisition Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Additional basis spread on variable rate Debt Instrument, Additional Basis Spread On Variable Rate Debt Instrument, Additional Basis Spread On Variable Rate Schedule of Debt Obligations Schedule of Debt [Table Text Block] Related and Nonrelated Parties [Axis] Related and Nonrelated Parties [Axis] Title Trading Arrangement, Individual Title Peer Group Total Shareholder Return Amount Peer Group Total Shareholder Return Amount Tax receivable agreement liability - related party Tax Receivable Agreement Liability, Noncurrent Tax Receivable Agreement Liability, Noncurrent Other long-term liabilities Other Noncurrent Liabilities [Member] Schedule of Identifiable Intangible Assets Schedule of Finite-Lived Intangible Assets [Table Text Block] Restatement Determination Date: Restatement Determination Date [Axis] Cash Payments to Acquire Businesses, Gross Non-PEO NEO Non-PEO NEO [Member] Letters of credit outstanding Letters of Credit Outstanding, Amount Contract liabilities Business Combination, Recognized Liability Assumed, Contract Liability Business Combination, Recognized Liability Assumed, Contract Liability Schedule of Prepaid Expenses And Other Current Assets Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Table Text Block] Schedule of Interest Rate Swap Agreements Schedule of Interest Rate Derivatives [Table Text Block] Sale of Stock [Axis] Sale of Stock [Axis] Gain reclassified from AOCI to Interest expense Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Name Trading Arrangement, Individual Name Award Type [Domain] Award Type [Domain] Effect of RSUs and stock options Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units Legence Holdings LLC Legence Holdings LLC [Member] Legence Holdings LLC Noncontrolling interests Equity, Attributable to Noncontrolling Interest Equity Awards Adjustments Equity Awards Adjustments [Member] Other Other Noncash Income (Expense) Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block] Installation & Maintenance Installation & Maintenance [Member] Installation & Maintenance Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Deferred offering costs included in Accounts payable Deferred Offering Costs Included In Accounts Payable Deferred Offering Costs Included In Accounts Payable Compensation Amount Outstanding Recovery Compensation Amount Principal amount Debt Instrument, Face Amount Tax receivable agreement liability and deferred taxes arising from exchanges of Class B Common Stock Tax Receivable Agreement Liability, Secondary Offering Exchanges Tax Receivable Agreement Liability, Secondary Offering Exchanges Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Statement of Comprehensive Income [Abstract] Recovery of Erroneously Awarded Compensation Disclosure [Line Items] Fair Value Estimate of Fair Value Measurement [Member] Contract liability revenue recognized during the period Contract with Customer, Liability, Revenue Recognized Accrued compensation and benefits Increase (Decrease) in Employee Related Liabilities Issuance of Legence Corp. Class A Common Stock Business Combination, Consideration Transferred, Equity Interest Bowers The Bowers Group, Inc. [Member] The Bowers Group, Inc. MNPI Disclosure Timed for Compensation Value MNPI Disclosure Timed for Compensation Value [Flag] Name Awards Close in Time to MNPI Disclosures, Individual Name AOCI, Net of Tax [Roll Forward] AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] Restricted Series C Common Interests Restricted Series C Interests [Member] Restricted Series C Interests 3.6995% Interest Rate Swap, Maturing at December 2028 3.6995% Interest Rate Swap, Maturing at December 2028 [Member] 3.6995% Interest Rate Swap, Maturing at December 2028 Weighted-average Class A Common Stock outstanding: Weighted Average Number of Shares Outstanding Reconciliation [Abstract] Aggregate Erroneous Compensation Not Yet Determined Aggregate Erroneous Compensation Not Yet Determined [Text Block] Employee Stock Employee Stock [Member] Revenue: Revenues [Abstract] Exchange of Class B Common Stock to Class A Common Stock Stock Issued During Period, Value, Conversion of Convertible Securities 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Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Statement of Financial Position Location, Balance [Domain] Statement of Financial Position Location, Balance [Domain] Inventories Inventory, Net Amortization of debt issuance costs and discounts Amortization of Debt Issuance Costs and Discounts Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Minimum Minimum [Member] Notes payable payments Repayments of Notes Payable Property and equipment, net of accumulated depreciation of $106,729 and $98,650 as of March 31, 2026 and December 31, 2025, respectively Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Company Selected Measure Name Company Selected Measure Name Business Combination, Pro Forma Information, Nonrecurring Adjustment, Acquisition-Related Cost Business Combination, Pro Forma Information, Nonrecurring Adjustment, Acquisition-Related Cost [Member] Decrease in contract liabilities Contract with Customer, Liability, Increase (Decrease) for Contract Acquired in Business Combination Deferred contract costs Deferred Costs, Current Fair Value Measurement [Domain] Fair Value Measurement [Domain] Total debt Long-Term Debt and Lease Obligation, Including Current Maturities Net loss attributable to Legence Business Combination, Pro Forma Information, Pro Forma Income (Loss), after Tax Debt Debt Disclosure [Text Block] Preferred stock, $0.01 par value, 50,000,000 shares authorized, no shares issued or outstanding as of March 31, 2026 and December 31, 2025 Preferred Stock, Value, Issued Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Accounts payable Accounts Payable, Current Stock Appreciation Rights (SARs) Stock Appreciation Rights (SARs) [Member] Liability Business Combination, Recognized Liability Assumed, Liability Net income attributable to Legence—diluted Net Income (Loss) Available to Common Stockholders, Diluted All Executive Categories All Executive Categories [Member] Common stock Common Stock, Value, Issued Carrying value of Goodwill Goodwill [Roll Forward] Professional Corporations Professional Corporations [Member] Professional Corporations Prepaid expenses and other current assets Business Combination, Recognized Asset Acquired, Prepaid Expense and Other Asset, Current Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Diluted (in shares) Weighted-average Class A Common Stock outstanding—diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Commitments and contingencies (Note 18) Commitments and Contingencies Non-GAAP Measure Description Non-GAAP Measure Description [Text Block] Intangible assets Business Combination, Recognized Asset Acquired, Identifiable Intangible Asset, Finite-Lived Business Combination [Axis] Business Combination [Axis] 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Class A [Member] Awards Close in Time to MNPI Disclosures, Table Awards Close in Time to MNPI Disclosures [Table Text Block] Revenue from Contract with Customer [Abstract] Hedging Designation [Axis] Hedging Designation [Axis] Total debt Debt Instrument, Fair Value Disclosure Operating lease liabilities, current and long-term Increase (Decrease) in Operating Lease Liability Total stockholders' equity Beginning balance Ending balance Equity, Including Portion Attributable to Noncontrolling Interest Document Type Document Type Level 3 Fair Value, Inputs, Level 3 [Member] Earnings Per Share Earnings Per Share [Text Block] Name Outstanding Recovery, Individual Name Loss Contingencies [Table] Loss Contingencies [Table] Additional paid-in capital Additional Paid in Capital Product and Service [Axis] Product and Service [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Revenue from Contract with Customer Benchmark Revenue from Contract with Customer Benchmark [Member] Revenue Revenue from Contract with Customer, Excluding Assessed Tax All Individuals All Individuals [Member] Long-Term Debt, Type [Domain] Long-Term Debt, Type [Domain] Fair Value Disclosures [Abstract] Purchases of property and equipment Payments to Acquire Property, Plant, and Equipment Name Forgone Recovery, Individual Name Total current assets Assets, Current Statistical Measurement [Axis] Statistical Measurement [Axis] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] Number of professional corporations contracted Number of Professional Corporations Contracted Number of Professional Corporations Contracted Line of credit facility, unused capacity, commitment fee (as percent) Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Weighted average interest rate Debt, Weighted Average Interest Rate Accounts receivable—other Other Receivables, Net, Current Effects of exercise of underwriters' overallotment option Stock Issued During Period, Shares, Conversion of Convertible Securities, Percent Stock Issued During Period, Shares, Conversion of Convertible Securities, Percent Cash tax savings (as percent) Tax Receivable Agreement, Cash Tax Savings Owed Tax Receivable Agreement, Cash Tax Savings Owed Fixed Interest Rate Derivative, Fixed Interest Rate Aggregate Erroneous Compensation Amount Aggregate Erroneous Compensation Amount Purchase price of common stock, percent Share-Based Compensation Arrangement by Share-Based Payment Award, Purchase Price of Common Stock, Percent Engineering & Consulting Engineering & Consulting [Member] Engineering & Consulting Peer Group Issuers, Footnote Peer Group Issuers, Footnote [Text Block] Net income attributable to Legence—basic Net income attributable to Legence—basic Net Income (Loss) Available to Common Stockholders, Basic (Decrease) increase 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Compensation Recovery Erroneously Awarded Compensation Recovery [Table] Accounts receivable, net Accounts Receivable, after Allowance for Credit Loss, Current Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Title of 12(b) Security Title of 12(b) Security Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Increase in tax receivable agreement liability Tax Receivable Agreement, Liability, Increase (Decrease) Tax Receivable Agreement, Liability, Increase (Decrease) Number of shares issued (in shares) Sale of Stock, Number of Shares Issued in Transaction Earnings per share: Earnings Per Share [Abstract] Maximum purchase shares during offering period Share-based Compensation Arrangement By Share-based Payment Award, Maximum Purchase Shares During Offering Period, Per Employee Share-based Compensation Arrangement By Share-based Payment Award, Maximum Purchase Shares During Offering Period, Per Employee Total other expense, net Nonoperating Income (Expense) Legence's ownership of Legence Holdings Common Units (as percent) Subsidiary, Ownership Percentage, Parent Variable Interest Entities and Equity Method Investments Equity Method Investments and Joint Ventures Disclosure [Text Block] Gross profit Gross profit Gross Profit Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Contract liabilities Increase (Decrease) in Contract with Customer, Liability Right-of-use asset modifications for operating leases Right-Of-Use Asset Modifications For Operating Leases Right-Of-Use Asset Modifications For Operating Leases Noncontrolling Interest [Abstract] Income taxes paid, net of refunds Income Taxes Paid, Net Contracts receivable, retentions Contracts Receivable, Retentions Contracts Receivable, Retentions 2028 Finite-Lived Intangible Asset, Expected Amortization, Year Two Award Timing Disclosures [Line Items] Long-term debt, gross Long-term debt, gross Long-Term Debt, Gross Contract liabilities Business Combination, Consideration Transferred, Deferred Consideration Business Combination, Consideration Transferred, Deferred Consideration Accrued compensation and benefits Employee-related Liabilities, Current Share-based payment, dividend Dividend, Share-Based Payment Arrangement Unrealized gain (loss) recognized in AOCI Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Property and equipment, net of accumulated depreciation of $106,729 and $98,650 as of March 31, 2026 and December 31, 2025, respectively Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization Weighted-average effect of dilutive securities (in shares) Incremental Common Shares Attributable To Dilutive Effect Of Conversion Of Stock Units Incremental Common Shares Attributable To Dilutive Effect Of Conversion Of Stock Units One Customer One Customer [Member] One Customer Stockholders' Equity Equity [Text Block] Trade names Trade Names [Member] Net income (loss) attributable to Legence Net Income (Loss) Attributable to Parent Contract liabilities Deferred Consideration, Current Deferred Consideration, Current Expiration Date Trading Arrangement Expiration Date Award type, percentage Share-Based Compensation Arrangement By Share-Based Payment Award, Award, Percentage Share-Based Compensation Arrangement By Share-Based Payment Award, Award, Percentage Other accrued liabilities Other Accrued Liabilities, Current Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Beginning balance Ending balance Limited Liability Company (LLC) Members' Equity, Including Portion Attributable to Noncontrolling Interest Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Adoption Date Trading Arrangement Adoption Date Base Rate Base Rate [Member] Compensation Actually Paid vs. Net Income Compensation Actually Paid vs. Net Income [Text Block] Total 2026 Acquisitions Total 2026 Acquisitions [Member] Total 2026 Acquisitions Accounts receivable, net Increase (Decrease) in Accounts Receivable Entity Current Reporting Status Entity Current Reporting Status Customer [Axis] Customer [Axis] Awards Close in Time to MNPI Disclosures Awards Close in Time to MNPI Disclosures [Table] Customer relationships Customer Relationships [Member] Income from operations Operating Income (Loss) Line of Credit Line of Credit [Member] Consolidated Entities [Domain] Consolidated Entities [Domain] Accumulated deficit Retained Earnings (Accumulated Deficit) Gain on sale of property and equipment Gain (Loss) on Disposition of Property Plant Equipment Contribution from Legence Parent for Series A Interests and Restricted Series C Interests Contributions From Parent I For Series A Interests And Restricted Series C Interests Contributions From Parent I For Series A Interests And Restricted Series C Interests Derivative liabilities Derivative Liability, Subject to Master Netting Arrangement, after Offset Statement of Financial Position [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Executive Category: Executive Category [Axis] Reasonable possible losses in excess of reserves established Loss Contingency, Accrual, Current Current Fiscal Year End Date Current Fiscal Year End Date Class of Stock [Axis] Class of Stock [Axis] Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table Aggregate Grant Date Fair Value of Equity Award Amounts Reported in Summary Compensation Table [Member] Schedule of Accounts Receivable Net Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Other income, net Other income, net Other Nonoperating Income (Expense) Statement [Table] Statement [Table] Interest rate swap instruments Derivative Liability Schedule of Consideration Transferred Business Combination [Table Text Block] Eligible employees contribution percentage Share-Based Compensation Arrangement by Share-Based Payment Award, Maximum Employee Subscription Rate Deferred taxes Deferred Income Tax Expense (Benefit) Adjustments to reconcile net income (loss) to cash provided by operating activities: Adjustment to 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in Contract with Customer, Asset Insider Trading Policies and Procedures Adopted Insider Trading Policies and Procedures Adopted [Flag] Measure: Measure [Axis] Self insurance coverage Self Insurance, Threshold For Stop-Loss Insurance Self Insurance, Threshold For Stop-Loss Insurance Thereafter Finite Lived Intangible Assets Amortization Expense After Year Four Finite Lived Intangible Assets Amortization Expense After Year Four Reclassification of vested Legence Parent Series A Interests from liabilities Adjustments To Member's Equity, Reclassification Of Vested Parent Interests From Liabilities Adjustments To Member's Equity, Reclassification Of Vested Parent Interests From Liabilities Underwriters option period Underwriters Option Period Underwriters Option Period Acquiree's revenue since acquisition date Business Combination, Acquiree's Revenue since Acquisition Date, Actual Basic (in shares) Weighted-average Class A Common Stock outstanding—basic (in shares) Weighted Average Number of Shares Outstanding, Basic Cost of revenue Cost of Product and Service Sold Schedule of Computation of Basic and Diluted EPS Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Credit agreement amendment fees Line Of Credit Facility, Amendment Fee, Amount Line Of Credit Facility, Amendment Fee, Amount Subsequent Events [Abstract] Segment Reporting [Abstract] Program & Project Management Program And Project Management [Member] Program And Project Management Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Debt Disclosure [Abstract] Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Derivative assets Derivative Asset, Subject to Master Netting Arrangement, after Offset Other expense (income): Nonoperating Income (Expense) [Abstract] Contribution from Legence Parent for Series A Interests and Restricted Series C Interests Adjustments To Additional Paid In Capital, 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liabilities Total liabilities Liabilities Deferred offering costs included in Accrued and other current liabilities Deferred Offering Costs Included In Accrued And Other Current Liabilities Deferred Offering Costs Included In Accrued And Other Current Liabilities Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] 3.3750% Interest Rate Swap, Maturing at December 2026 3.3750% Interest Rate Swap, Maturing at December 2026 [Member] 3.3750% Interest Rate Swap, Maturing at December 2026 Line of credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Net assets acquired based on fair values: Business Combination, Recognized Asset Acquired to Liability Assumed, Excess (Less), and Goodwill [Abstract] Pension Adjustments Prior Service Cost Pension Adjustments Prior Service Cost [Member] Prepaid expenses Prepaid Expense, Current Operating Expenses [Abstract] 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[Member] Accrued and other current liabilities Business Combination, Recognized Liability Assumed, Liability, Accrued And Other Liabilities, Current Business Combination, Recognized Liability Assumed, Liability, Accrued And Other Liabilities, Current Increase in cash and cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Notes payable Notes Payable, Current