Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating Activities
Net loss	$ (5,934)	$ (3,605)
Adjustments to reconcile net loss to net cash used in operating activities:
(Gain) from change in fair value of derivative warrant liability	(3,226)	(5,248)
Loss from change in fair value of the 2017 Notes	339	836
Loss on exchange or conversion of debt	964
(Gain) on extinguishment of warrant liability	(33)
Stock-based compensation	128	358
Depreciation and amortization	1,676	1,621
Non-cash interest expense	80	1,057
Changes in operating assets and liabilities:
Accounts receivable	(82)	523
Inventories	(720)	500
Prepaid expenses and other current assets	(11)	(278)
Accounts payable, accrued expenses, and long-term liabilities	(1,228)	(1,268)
Net cash used in operating activities	(8,047)	(5,504)
Investing Activities
Acquisitions of property, plant and equipment	(673)	(2,247)
Net cash used in investing activities	(673)	(2,247)
Financing Activities
Payments on secured debt	(9,616)	(84)
Debt and equity offering costs	(205)	(589)
Proceeds from issuance of common stock and common stock warrants	11,044
Proceeds from the exercise of warrants	2	65
Net cash provided (used) by financing activities	1,225	(608)
Net decrease in cash and cash equivalents	(7,495)	(8,359)
Cash and cash equivalents
Beginning of period	27,888	17,031
End of period	20,393	8,672
Supplemental disclosures of cash and non-cash investing and financing transactions
Cash paid for interest, net of interest capitalized	1,616	1,503
Non-cash purchase of property, plant and equipment	461	2,049
Exchange of convertible debt into common stock	8,177
Accrued offering costs	73	$ 59
Fair value of warrants at issuance and upon exercise, net	$ 5,503