Quarterly report pursuant to Section 13 or 15(d)

Revenue - Additional Information (Details)

v3.8.0.1
Revenue - Additional Information (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2018
USD ($)
Revenue Recognition [Abstract]  
Payment term on product sales 30 days
Payment term on installation services 30 days
Payment term on contractually determined milestones 30 days
Payment term on energy production contract invoices 30 days
Revenue recognized that was in unbilled revenue at beginning of period $ 2.6
Revenue billed this period that had been recognized in previous periods 1.8
Deferred Revenue, Revenue Recognized 1.6
Cash payments received in advance of satisfying performance obligations 1.5
Remaining performance obligations $ 1.8
Performance obligation revenue expected to be recognized over the next 24 months (percent) 99.00%
Performance obligation revenue to be recognized in first 12 months (percent) 77.00%
Performance obligation revenue to be recognized over the subsequent 12 months (percent) 22.00%