Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (12,612)	$ (10,615)
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 and common stock adjustment feature liabilities	8,495	1,900
Offering costs		904
Depreciation and amortization	34	52
Lease amortization	172
Gain on disposal of equipment		(3)
Net amortization of investment premium	(39)	(2)
Stock-based compensation	422	298
Changes in operating assets and liabilities:
Accounts receivable	86	1,179
Unbilled revenue	3	(45)
Inventories	39	21
Prepaid expenses and other current assets	197	137
Accounts payable and accrued expenses	(538)	(322)
Amounts due to related parties	(16)	(25)
Unearned revenue	(40)	(96)
Operating lease payments	(172)
Net cash used in operating activities	(3,969)	(2,617)
CASH FLOWS FROM INVESTING ACTIVITIES:
Proceeds from sale of property and equipment		9
Purchases of property and equipment	(88)	(33)
Purchases of investments	(6,690)
Proceeds from sales and maturities of investments	9,200	3,900
Net cash provided by investing activities	2,422	3,876
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		(932)
Payments of offering costs relating to June Offering	(16)
Payments of deferred offering costs	(5)
Proceeds from exercise of stock options and ESPP purchases	8	966
Net cash (used in) provided by financing activities	(13)	10,034
Net (decrease) increase in cash and cash equivalents	(1,560)	11,293
Cash and cash equivalents — beginning of period	11,998	9,125
Cash and cash equivalents — end of period	10,438	20,418
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes	2	24
NONCASH INVESTING AND FINANCING ACTIVITIES:
Offering costs in accounts payable and accrued expenses at end of period	7	334
Deferred offering costs in accounts payable and accrued expenses at end of period	18
Common stock warrants issued to placement agent and included in offering costs related to Purchase Agreement		526
Right of use assets obtained in exchange for new operating lease liabilities	2,328
Proceeds from sale of fixed assets included in prepaid expenses and other current assets at end of period		$ 1
Purchases of fixed assets included in accounts payable and accrued expenses	$ 13