Investment in Laramie Energy, LLC - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
ASSETS
Current assets	$ 636,469				$ 1,032,174				$ 636,469	$ 1,032,174
Current liabilities	878,680				1,034,322				878,680	1,034,322
Revenue
Income (loss) from operations	(114,132)	$ 2,750	$ (25,443)	$ (181,173)	59,531	$ 18,405	$ 48,621	$ 21,423	(317,998)	147,980	$ 81,941
Net income (loss)	(131,918)	$ (14,271)	$ (40,560)	$ (222,337)	35,439	$ (83,891)	$ 28,169	$ 61,092	(409,086)	40,809	39,427
Laramie Energy Company
ASSETS
Current assets	34,573				23,367				34,573	23,367
Non-current assets	355,538				393,575				355,538	393,575
Current liabilities	217,523				229,687				217,523	229,687
Non-current liabilities	$ 93,193				$ 85,287				93,193	85,287
Revenue
Natural gas and oil revenues									121,893	193,906	226,974
Income (loss) from operations									(2,994)	(360,967)	34,206
Net income (loss)									$ (22,589)	$ (380,473)	$ 6,347