Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities:
Net loss	$ (11,643)	$ (8,429)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	693	503
Amortization expense - right-of-use assets - operating and finance leases	1,486
Loss (Gain) on disposal of property and equipment	(1)	1
Stock-based compensation	4,051	4,437
Unrealized loss (gain) on investment in equity securities	168	(5)
Changes in operating assets and liabilities:
Accounts receivable, net	(262)	3,057
Unbilled receivables	365	(103)
Inventories	(131)	0
Prepaid expenses and other current assets	(882)	(132)
Contract assets	35	(554)
Other non-current assets	59	79
Accounts payable	(1,625)	(530)
Accrued compensation	(721)	(936)
Other accrued liabilities	402	451
Other long term liabilities	(715)	(514)
Deferred revenue	812	(9,466)
Net cash used in operating activities	(7,909)	(12,141)
Investing activities:
Purchase of property and equipment	(1,258)	(1,472)
Proceeds from disposal of property and equipment	1	0
Net cash used in investing activities	(1,257)	(1,472)
Financing activities:
Proceeds from exercises of stock options	2,843	1,858
Proceeds from issuance of common stock in connection with public offering, net of underwriting discounts and commission	0	37,497
Proceeds from issuance of common stock in connection with private placement	50,000	0
Payments of lease obligations - Finance leases	(119)	(118)
Taxes paid related to net share settlement of equity awards	(2,799)	(3,140)
Net cash provided by financing activities	49,851	35,918
Net increase in cash, cash equivalents and restricted cash	40,685	22,305
Cash, cash equivalents and restricted cash at the beginning of the period	54,485	32,776
Cash, cash equivalents and restricted cash at the end of the period	95,170	55,081
Supplemental disclosure of cash flow information
Interest paid	9	42
Income taxes paid	0	5
Purchase of property and equipment recorded in accounts payable and accrued expenses	773	67
Cash and cash equivalents	93,421	53,621
Total cash, cash equivalents and restricted cash at the end of the period	54,485	32,776
IPO [Member]
Financing activities:
Costs incurred in connection with public placement	0	(179)
Private Placement [Member]
Financing activities:
Costs incurred in connection with public placement	$ (74)	$ 0