Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Property, Plant and Equipment
Total property, plant and equipment, net	$ 79,364		$ 73,226
Depreciation expense	29	$ 26
Non project assets
Property, Plant and Equipment
Property, plant and equipment, gross	605		579
Less: accumulated depreciation	(400)		(371)
Total property, plant and equipment, net	205		208
Computers
Property, Plant and Equipment
Property, plant and equipment, gross	82		69
Furniture, fixtures, and equipment
Property, Plant and Equipment
Property, plant and equipment, gross	257		246
Leasehold improvements
Property, Plant and Equipment
Property, plant and equipment, gross	266		264
Project assets
Property, Plant and Equipment
Project assets in progress	79,159		73,018
Rio Grande
Property, Plant and Equipment
Project assets in progress	68,591		62,866
Rio Bravo
Property, Plant and Equipment
Project assets in progress	$ 10,568		$ 10,152