Organization and Accounting Policies (Rollforward of Aggregate Allowance for Bad Debt) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Organization and Accounting Policies [Abstract]
Balance at beginning of period	$ (2,273)	$ (1,508)
Bad debt charge	(101)	(810)
Adjustment associated with reversal of allowance on Mutamba receivable		593
Adjustment associated with Sasol acquisition	(2,879)
Foreign currency gain (loss)	161
Balance at end of period	$ (5,092)	$ (1,725)