Revenues from Contracts with Customers - Summary of Company's Revenue by Major Source (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 148,127	$ 100,221	$ 104,016
RNG [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	132,227	83,556	84,389
REG [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	15,900	16,665	19,627
Natural Gas Commodity [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	47,321	29,458	32,185
Natural Gas Environmental Attributes [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	84,906	54,098	52,204
Electric Commodity [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	9,692	9,642	12,396
Electric Environmental Attributes [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	6,208	7,023	7,231
Goods transferred at a point in time [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	106,292	68,112	66,026
Goods transferred at a point in time [Member] | RNG [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	100,084	61,089	58,795
Goods transferred at a point in time [Member] | REG [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	6,208	7,023	7,231
Goods transferred at a point in time [Member] | Natural Gas Commodity [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	15,178	6,991	6,591
Goods transferred at a point in time [Member] | Natural Gas Environmental Attributes [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	84,906	54,098	52,204
Goods transferred at a point in time [Member] | Electric Environmental Attributes [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	6,208	7,023	7,231
Goods transferred over time [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	41,835	32,109	37,990
Goods transferred over time [Member] | RNG [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	32,143	22,467	25,594
Goods transferred over time [Member] | REG [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	9,692	9,642	12,396
Goods transferred over time [Member] | Natural Gas Commodity [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	32,143	22,467	25,594
Goods transferred over time [Member] | Electric Commodity [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 9,692	$ 9,642	$ 12,396