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Investments in Other Entities and Noncontrolling Interest in a Subsidiary - NG Advantage (Details) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Feb. 29, 2020
Feb. 06, 2020
Oct. 01, 2018
Feb. 28, 2018
Feb. 28, 2019
Feb. 28, 2019
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Jun. 24, 2020
Oct. 14, 2014
Schedule of Equity Method Investments [Line Items]                      
Outstanding balance             $ 265,367,000 $ 261,161,000      
Payments to acquire additional controlling interest             32,892,000 73,450,000 $ 89,700,000    
Loss from noncontrolling interest             (619,000) (601,000) (857,000)    
Impairment of investments in equity securities             8,102,000 0 0    
Investments carried at cost             $ 0 8,000,000      
NG Advantage                      
Schedule of Equity Method Investments [Line Items]                      
Ownership interest after transaction (as a percent)             93.30%        
NG Advantage                      
Schedule of Equity Method Investments [Line Items]                      
Ownership interest acquired                     53.30%
Purchase of interest by parent, shares purchased (in shares)     1,000,001                
Debt issuance amount             $ 0 $ 29,100,000      
Outstanding balance             47,500,000        
Ownership interest before transaction (as a percent)   64.60% 53.50% 53.30%              
Ownership interest after transaction (as a percent)   93.20% 61.70% 53.50%   64.60%   93.30%      
Payments to acquire additional controlling interest     $ 5,000,000                
Loss from noncontrolling interest             (600,000) $ (600,000) $ 900,000    
Noncontrolling interest, fair value             $ 6,300,000 $ 6,900,000      
NG Advantage | Payment Obligations                      
Schedule of Equity Method Investments [Line Items]                      
Purchase of interest by parent, shares purchased (in shares)       19,660 100,000 400,000          
NG Advantage | Convertible Promissory Note November2019 [Member]                      
Schedule of Equity Method Investments [Line Items]                      
Number of common units to be called by warrants (in shares)                 2,086,879    
Debt issuance amount                 $ 26,700,000    
Common unit purchase agreement | NG Advantage                      
Schedule of Equity Method Investments [Line Items]                      
Issuance of equity by subsidiary to parent (in shares) 283,019                    
Ownership interest after transaction (as a percent)             93.30%        
Long-Term Natural Gas Purchase Contracts | NG Advantage | BP Products North America                      
Schedule of Equity Method Investments [Line Items]                      
Contingent consideration, liability (up to)       $ 30,000,000           $ 15,000,000