Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (12,834)	$ (12,747)
Adjustments to reconcile net loss to cash used in operating activities:
Initial loss on common stock warrant and common stock adjustment feature liabilities	4,000
Change in fair value of common stock warrant liabilities and common stock adjustment feature liability	(5,986)
Offering costs	2,544
Depreciation and amortization	123	215
Gain on disposal of equipment	(3)	(3)
Net amortization of investment premium	(115)	(82)
Stock-based compensation	998	1,177
Loss on sale of investments		2
Accretion of debt discount		98
Loss on extinguishment of debt		900
Changes in operating assets and liabilities:
Accounts receivable	1,038	276
Unbilled revenue	(164)	123
Inventories	301	164
Prepaid expenses and other current assets	(334)	(222)
Other noncurrent assets		(245)
Accounts payable and accrued expenses	(142)	(496)
Amounts due to related parties	(11)	1
Unearned revenue	(351)	(443)
Net cash used in operating activities	(10,936)	(11,282)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sale of property and equipment	10	4
Purchases of property and equipment	(89)	(77)
Purchases of investments	(22,871)	(19,405)
Proceeds from sales and maturities of investments	8,950	57,778
Net cash (used in) provided by investing activities	(14,000)	38,300
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock and warrants from Purchase Agreement	10,000
Payments of offering costs relating to Purchase Agreement	(1,308)
Proceeds from issuance of common stock and warrants from June Offering	14,000
Payments of offering costs relating to June Offering	(1,181)
Payment of debt extinguishment costs		(1,125)
Proceeds from exercise of stock options and ESPP purchases	969	24
Payment on notes payable		(25,000)
Net cash provided by (used in) financing activities	22,480	(26,101)
Net (decrease) increase in cash and cash equivalents	(2,456)	917
Cash and cash equivalents — beginning of period	9,125	2,013
Cash and cash equivalents — end of period	6,669	2,930
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for interest		746
Cash paid for income taxes	24	2
NONCASH INVESTING AND FINANCING ACTIVITIES:
Common stock warrants issued to placement agent and included in offering costs related to Purchase Agreement	526
Common stock warrants issued to placement agent and included in offering costs related to June Offering	239
Purchases of property and equipment included in accounts payable and accrued expenses		2
Reclassification of common stock adjustment feature liability balance to equity	$ 8,378
Exchange of membership interest in unconsolidated entity for common stock		$ 2