Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands			3 Months Ended		9 Months Ended		12 Months Ended
	May 09, 2025 USD ($)	Jul. 21, 2022 shares	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) segment variable_interest_entity shares	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($) shares	Jun. 30, 2025 USD ($)	Mar. 31, 2025 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Derivative [Line Items]
Number of variable interest entities | variable_interest_entity					12
Number of operating segments | segment					3
Product warranty accrual, current			$ 280		$ 280		$ 171
Gain (loss) on earnout awards			0	$ 278	281	$ 1,457
Business combination, contingent consideration, liability, noncurrent			23		23		$ 304
Revenue recognized included in contract liabilities					5,006	3,746
Backlog			51,484		51,484
Net proceeds from the sale of tax credits			14,567	8,906	36,290	8,906
Legal and insurance fees			$ 1,873	$ 1,182	$ 4,510	$ 1,182
Accounts Payable | Supplier Concentration Risk | One Vendor
Derivative [Line Items]
Concentration risk percentage					10.00%		17.00%
One Customer | Revenue Benchmark | Customer Concentration Risk
Derivative [Line Items]
Concentration risk percentage			34.00%		38.00%
Two Customers | Revenue Benchmark | Customer Concentration Risk
Derivative [Line Items]
Concentration risk percentage				56.00%		54.00%
Two Customers | Accounts Receivable | Customer Concentration Risk
Derivative [Line Items]
Concentration risk percentage					55.00%		50.00%
Fuel Station Services
Derivative [Line Items]
Environmental credits held for sale			$ 4,515	$ 1,443	$ 15,055	$ 8,293
Class B And D Ordinary Share | Opal Fuels
Derivative [Line Items]
Stock issued (in shares) | shares		144,399,037
Redeemable non-controlling interests
Derivative [Line Items]
Redeemable non-controlling interests			$ 342,528	$ 519,373	$ 342,528	$ 519,373	$ 482,863	$ 365,548	$ 276,719	$ 597,069	$ 705,190	$ 802,720
Sponsor Letter Agreement
Derivative [Line Items]
Percentage of common stock subject to vesting and forfeiture conditions		10.00%
Common stock subject to vesting and forfeiture conditions, period		60 months
Reverse recapitalization, number of shares subject to forfeiture shares (in shares) | shares					716,650		716,650
Opal Fuels
Derivative [Line Items]
Capital contributions	$ 4,646
Third-Party Partner
Derivative [Line Items]
Capital contributions	$ 1,998
RNG Facility
Derivative [Line Items]
Subsidiary, ownership percentage, parent	70.00%
Subsidiary ownership percentage, counterparty	30.00%
Noncontrolling interest	$ 1,998