Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (17,284)	$ (8,222)
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	2,435
Offering costs	2,543
Depreciation and amortization	98	146
Gain on disposal of equipment	(3)	(3)
Net amortization of investment premium	(27)	(65)
Stock-based compensation	656	760
Accretion of debt discount		99
Changes in operating assets and liabilities:
Accounts receivable	1,051	(83)
Unbilled revenue	(102)	43
Inventories	226	140
Prepaid expenses and other current assets	(245)	(603)
Other noncurrent assets		(327)
Accounts payable and accrued expenses	(52)	(525)
Amounts due to related parties	(17)	(3)
Unearned revenue	(197)	(274)
Net cash used in operating activities	(6,918)	(8,917)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sale of property and equipment	9	4
Purchases of property and equipment	(68)	(58)
Purchases of investments	(18,908)	(19,405)
Proceeds from sales and maturities of investments	3,900	39,785
Net cash (used in) provided by investing activities	(15,067)	20,326
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	(1,305)
Proceeds from issuance of common stock and warrants from June Offering	14,000
Payments of offering costs relating to June Offering	(1,134)
Proceeds from exercise of stock options and ESPP purchases	966	16
Net cash provided by financing activities	22,527	16
Net increase in cash and cash equivalents	542	11,425
Cash and cash equivalents — beginning of period	9,125	2,013
Cash and cash equivalents — end of period	9,667	13,438
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for interest		599
Cash paid for income taxes	24	1
NONCASH INVESTING AND FINANCING ACTIVITIES:
Proceeds from sale of fixed assets included in prepaid expenses and other current assets at end of period	1
Offering costs in accounts payable and accrued expenses at end of period	46
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
Reclassification of common stock adjustment feature liability balance	$ 8,378
Exchange of membership interest in unconsolidated entity for common stock		$ 2