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Income Taxes - Company's net deferred tax assets (Details) - USD ($)
Dec. 31, 2020
Dec. 31, 2019
Deferred tax assets:    
Net-operating loss carryforward $ (59,960,000) $ (50,821,000)
Total gross deferred tax assets 93,011,000 74,955,000
Valuation allowance 91,315,000 73,930,000
Star Peak Energy Transition Corp [Member]    
Deferred tax assets:    
Net-operating loss carryforward (13,291) (176)
Start-up/Organization costs (693,037) (2,009)
Total gross deferred tax assets 706,328 2,185
Valuation allowance $ 706,328 $ 2,185