Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 1,093	$ 2,279
Deposits	498	1,336
Future proceeds from sale of Magellan Petroleum UK (Note 3)	4,969	0
Tradable equity securities (Note 3)	3,731	0
Derivative asset, current (Note 6)	3,209	0
Other current assets	198	291
Total prepaid expenses and other current assets	$ 13,698	$ 3,906