Investment in Laramie Energy, LLC - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
ASSETS
Current assets	$ 497,512		$ 497,512		$ 403,108
Current liabilities	458,273		458,273		382,765
REVENUE
Income (loss) from operations	26,716	$ (21,784)	72,356	$ (44,819)
Net income (loss)	18,824	(27,761)	53,616	(59,522)
Laramie Energy Company
ASSETS
Current assets	12,149		12,149		12,199
Non-current assets	690,600		690,600		655,022
Current liabilities	43,599		43,599		58,067
Non-current liabilities	213,517		213,517		$ 186,631
REVENUE
Natural gas and oil revenues	38,141	31,091	114,178	68,513
Income (loss) from operations	133	(4,929)	(162)	(28,282)
Net income (loss)	$ (1,838)	$ 5,056	$ 18,102	$ (41,183)