Accrued Liabilities and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accrued Liabilities and Other Current Liabilities
Employee compensation expense	$ 651	$ 1,851
Project asset costs	4,471	3,317
Accrued legal services	75	141
Other accrued liabilities	272	547
Total accrued liabilities and other current liabilities	$ 5,469	$ 5,856