Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Summary of Significant Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents, and Restricted Cash	As of December 31, 2021 2020 (in thousands)Cash and cash equivalents $48,675 $47,853Restricted cash - current 79 86Restricted cash - non-current 1,752 925Abandonment funding 21,808 12,453Total cash, cash equivalents and restricted cash $72,314 $61,317
Analysis of Change in Allowance for Doubtful Accounts	Year Ended December 31, 2021 2020 2019 (in thousands)Allowance for bad debt Balance at beginning of period $ (2,273) $ (1,508) $ (2,535)Bad debt (charge) income, net of receipts (875) (1,165) 341Adjustment associated with reversal of allowance on Mutamba receivable — 593 623Adjustment associated with Sasol Acquisition (2,879) — —Foreign currency gain (loss) 286 (193) 63Balance at end of period $ (5,741) $ (2,273) $ (1,508)
Assets and Liabilities Measured on Recurring Basis	As of December 31, 2021 Balance Sheet Line Level 1 Level 2 Level 3 Total (in thousands)Liabilities SARs liabilityAccrued liabilities $ — $ 609 $ — $ 609Derivative liability - crude oil swapsAccrued liabilities — 4,806 — 4,806 $ — $ 5,415 $ — $ 5,415 As of December 31, 2020 Balance Sheet Line Level 1 Level 2 Level 3 Total (in thousands)Liabilities SARs liabilityAccrued liabilities $ — $ 2,289 $ — $ 2,289SARs liabilityOther long-term liabilities — 193 — 193 $ — $ 2,482 $ — $ 2,482