Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net loss	$ (8,429)	$ (13,740)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	503	554
Gain on disposal of property and equipment	1	(3)
Income tax benefit related to marketable securities	0	(60)
Stock-based compensation	4,437	3,379
Unrealized gain on investment in marketable securities	(5)	0
Changes in operating assets and liabilities:
Accounts receivable, net	2,954	(1,879)
Inventories, net	0	19
Prepaid expenses and other current assets	(132)	(1,824)
Contract Assets	(554)	0
Other assets	79	(44)
Accounts payable	(530)	(446)
Accrued compensation	(936)	(1,394)
Other accrued liabilities	451	271
Long term lease incentive	(212)	(212)
Other long term liabilities	(302)	(56)
Deferred revenue	(9,466)	3,904
Net cash used in operating activities	(12,141)	(11,531)
Investing activities:
Purchase of property and equipment	(1,472)	(680)
Proceeds from disposal of property and equipment	0	3
Net cash used in investing activities	(1,472)	(677)
Financing activities:
Proceeds from exercises of stock options	1,858	142
Proceeds from issuance of common stock in connection with public offering, net of underwriting discounts and commission	37,497	23,782
Costs incurred in connection with public offering	(179)	(491)
Principal payments on capital lease obligations	(118)	(60)
Taxes paid related to net share settlement of equity awards	(3,140)	(1,636)
Net cash provided by financing activities	35,918	21,737
Net increase in cash, cash equivalents and restricted cash	22,305	9,529
Cash, cash equivalents and restricted cash at the beginning of the period	32,776	20,864
Cash, cash equivalents and restricted cash at the end of the period	55,081	30,393
Supplemental disclosure of cash flow information:
Interest paid	42	117
Income taxes paid	5	5
Supplemental non-cash investing and financing activities:
Equipment acquired under capital leases	0	840
Purchase of property and equipment recorded in accounts payable and accrued expenses	67	34
Cash and cash equivalents	53,621	28,817
Total cash, cash equivalents and restricted cash at the end of the period	$ 32,776	$ 20,864