Noncontrolling Interests - Schedule of Ownership of Legence Holdings (Details) - Legence Holdings LLC - shares	3 Months Ended
Mar. 31, 2026	Dec. 31, 2025
Noncontrolling Interest [Line Items]
Common unit, outstanding (in shares)	105,336,929
Issuance of Class A Common Stock for acquisitions (in shares)	2,701,003
Effects of exercise of underwriters' overallotment option (in shares)	0
Common unit, outstanding (in shares)	108,037,932
Legence's ownership of Legence Holdings Common Units (as percent)	100.00%	100.00%
Issuance of Class A Common Stock for acquisitions	0.00%
Effects of exercise of underwriters' overallotment option	0.00%
LGN A Units
Noncontrolling Interest [Line Items]
Common unit, outstanding (in shares)	63,856,975
Issuance of Class A Common Stock for acquisitions (in shares)	2,701,003
Effects of exercise of underwriters' overallotment option (in shares)	780,121
Common unit, outstanding (in shares)	67,338,099
Legence's ownership of Legence Holdings Common Units (as percent)	62.30%	60.60%
Issuance of Class A Common Stock for acquisitions	1.00%
Effects of exercise of underwriters' overallotment option	0.70%
LGN B Units
Noncontrolling Interest [Line Items]
Common unit, outstanding (in shares)	41,479,954
Issuance of Class A Common Stock for acquisitions (in shares)	0
Effects of exercise of underwriters' overallotment option (in shares)	(780,121)
Common unit, outstanding (in shares)	40,699,833
Legacy Owners ownership of Legence Holdings Common Units (as percent)	37.70%	39.40%
Issuance of Class A Common Stock for acquisitions	(1.00%)
Effects of exercise of underwriters' overallotment option	(0.70%)

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