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Revenue Recognition - Narrative (Details)
3 Months Ended
Mar. 31, 2019
utlity_company
Cogeneration_facilities
Revenue from Contract with Customer [Abstract]  
Payment term (within) 30 days
Number of cogeneration facilities selling majority of electric output not used in operations | Cogeneration_facilities 3
Number of utility companies under long term contract to buy electrical output | utlity_company 2