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