Nature of Operations - Liquidity (Details)
$ in Thousands
 1 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2016
USD ($)
Oct. 31, 2016
USD ($)
Dec. 31, 2016
USD ($)
Sep. 30, 2016
USD ($)
Jun. 30, 2016
USD ($)
Mar. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Sep. 30, 2015
USD ($)
Jun. 30, 2015
USD ($)
Mar. 31, 2015
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
item
Dec. 23, 2016
USD ($)
Jun. 27, 2016
USD ($)
Mar. 02, 2016
USD ($)
Dec. 31, 2013
USD ($)
Liquidity                                  
Net loss attributable to common shareholders     $ 19,237 $ 13,420 $ 13,154 $ 11,780 $ 25,227 $ 10,238 $ 9,253 $ 11,077 $ 57,591 $ 55,795 $ 88,644        
Accumulated deficit $ 1,051,467   1,051,467       993,876       1,051,467 993,876          
Net cash used in operating activities                     29,636 47,274 40,780        
Net loss attributable to the Company                     57,487 55,690 88,488        
Impact of noncash charges/gains                     10,900            
Net inflows from fluctuations in working capital and other assets and liabilities                     16,900            
Cash and cash equivalents 46,014   46,014       63,961       46,014 63,961 146,205       $ 5,027
Net working capital 44,400   44,400       $ 88,500       44,400 88,500          
Remaining lease payment 51,507   51,507               51,507            
Cash added to the restricted accounts   $ 12,000                              
Gross proceeds from shares of common stock sold in an underwritten public offering                     30,000   176,700        
Net proceeds from public offering 11,900                   27,500   165,700        
Proceeds from Warrant Exercises                     $ 111 $ 25 $ 18,340        
Number of Underwritten Public Offerings | item                         3        
Minimum period for which we believe that our current cash, cash equivalents, cash generated from future sales, and cash generated from the exercise of outstanding warrants will provide sufficient liquidity to fund operations                     1 year            
Generate Lending, LLC                                  
Liquidity                                  
Short-term borrowing                               $ 25,000  
Debt issuance costs                               $ 1,300  
Hercules Capital, Inc.                                  
Liquidity                                  
Long-term borrowings                             $ 25,000    
Debt issuance costs                             $ 1,400    
NY Green Bank                                  
Liquidity                                  
Long-term borrowings $ 25,000   $ 25,000               $ 25,000     $ 25,000      
Debt issuance costs                           $ 1,200