Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Property, Plant and Equipment
Total property, plant and equipment, net	$ 86,060		$ 86,060		$ 73,226
Depreciation expense	48	$ 26	77	$ 52
Non project assets
Property, Plant and Equipment
Property, plant and equipment, gross	721		721		579
Less: accumulated depreciation	(448)		(448)		(371)
Total property, plant and equipment, net	273		273		208
Computers
Property, Plant and Equipment
Property, plant and equipment, gross	115		115		69
Furniture, fixtures, and equipment
Property, Plant and Equipment
Property, plant and equipment, gross	289		289		246
Leasehold improvements
Property, Plant and Equipment
Property, plant and equipment, gross	317		317		264
Project assets
Property, Plant and Equipment
Project assets in progress	85,787		85,787		73,018
Rio Grande
Property, Plant and Equipment
Project assets in progress	74,719		74,719		62,866
Rio Bravo
Property, Plant and Equipment
Project assets in progress	$ 11,068		$ 11,068		$ 10,152