Investment in Laramie Energy, LLC - Summarized Financial Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
ASSETS
Current assets	$ 456,716		$ 456,716		$ 403,108
Current liabilities	427,956		427,956		382,765
REVENUE
Loss from operations	16,451	$ (3,313)	45,640	$ (23,035)
Net income (loss)	7,006	(13,088)	34,792	(31,761)
Laramie Energy Company
ASSETS
Current assets	10,865		10,865		12,199
Non-current assets	667,583		667,583		655,022
Current liabilities	39,909		39,909		58,067
Non-current liabilities	192,737		192,737		$ 186,631
REVENUE
Natural gas and oil revenues	35,425	22,729	76,037	37,422
Loss from operations	(1,458)	(12,229)	(295)	(23,353)
Net income (loss)	$ 2,412	$ (43,660)	$ 19,940	$ (46,239)