Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (16,240)	$ (15,292)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	322	1,933
Warrant liability revaluation income	(4,920)	(11,884)
Derivative liability revaluation expense	1,407	462
Loss on disposal or impairment of property and equipment	40	69
Depreciation and amortization	384	564
Amortization of discount on convertible debt converted to common shares	86	0
Intangible asset impairment	0	3,905
Recovery of doubtful accounts	0	(12)
Loss on write-down of inventory	0	356
Decrease (increase) in operating assets:
Accounts receivable	0	12
Inventory	0	126
Prepaid expenses and other current assets	28	796
Other assets	26	(65)
Increase (decrease) in operating liabilities:
Accounts payable	69	(139)
Related party payable	1,361	(9,778)
Accrued expenses and deferred rent	(342)	(214)
Accrued interest payable	742	228
Deferred revenue	0	(457)
Net cash used in operating activities	(17,037)	(29,390)
Cash flows from investing activities:
Purchase of property and equipment	(433)	(253)
Proceeds from the sale of property and equipment	0	1
Net cash used in investing activities	(433)	(252)
Cash flows from financing activities:
Proceeds from private placement, net	7,623	17,933
Proceeds from common stock offering, net	9,749	0
Payment of deferred offering costs	0	(42)
Principal payments on capital lease obligations	0	(2)
Net cash provided by financing activities	17,372	17,889
Net decrease in cash and cash equivalents	(98)	(11,753)
Cash and cash equivalents, beginning of period	17,515	29,268
Cash and cash equivalents, end of period	17,417	17,515
Noncash Investing and Financing Items [Abstract]
Property and equipment in accounts payable	29	57
Offering costs in accounts payable and accrued expenses	444	23
Reduction of warrant liability upon cashless exercise of warrants	41	0
Reduction of accrued interest payable upon cashless exercise of promissory notes	3	0
Reduction in derivative liability upon cashless exercise of promissory notes	6	0
Cashless exercise of promissory notes	85	0
Dividend paid in-kind to preferred stockholders	264	0
Deemed dividend on preferred stock	$ 4,099	$ 0