Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net loss	$ (10,878)	$ (22,996)	$ (8,558)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of intangible assets	0	0	2,812
Depreciation	1,147	1,042	1,734
Stock-based compensation	7,889	7,091	5,673
Loss (gain) on disposal of property and equipment	8	9	(42)
Loss on investment securities	83	0	0
Gain from extinguishment of asset retirement obligation	0	(207)	0
Changes in operating assets and liabilities:
Accounts receivable, net	960	(5,298)	1,405
Inventories	447	(210)	167
Prepaid expenses and other current assets	(37)	157	7
Contract assets	(35)	0	0
Unbilled receivables	(2,349)	(353)	0
Other non-current assets	228	(44)	52
Accounts payable	(524)	(801)	942
Accrued compensation	519	439	983
Other accrued liabilities	(17)	1,399	(593)
Other long-term liabilities	(904)	0	0
Deferred revenue	(10,631)	11,017	(6,442)
Net cash used in operating activities	(14,094)	(8,755)	(1,860)
Investing activities:
Purchase of property and equipment	(2,768)	(985)	(888)
Proceeds from disposal of property and equipment	2	2	42
Net cash used in investing activities	(2,766)	(983)	(846)
Financing activities:
Proceeds from exercises of stock options	4,680	266	1,034
Proceeds from issuance of common stock in connection with public offering, net of underwriting discounts and commission	37,497	23,782	0
Costs incurred in connection with public offering	(180)	(553)	0
Principal payments on capital lease obligations	(238)	(175)	0
Taxes paid related to net share settlement of equity awards	(3,190)	(1,670)	(1,524)
Net cash provided by (used in) financing activities	38,569	21,650	(490)
Net increase (decrease) in cash, cash equivalents and restricted cash	21,709	11,912	(3,196)
Cash, cash equivalents and restricted cash at the beginning of the year	32,776	20,864	24,060
Cash, cash equivalents and restricted cash at the end of the year	54,485	32,776	20,864
Supplemental disclosure of cash flow information:
Interest paid	84	141	14
Income taxes	5	32	5
Supplemental non-cash financing activities:
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	0	862	0
Capital expenditures incurred but not yet paid	300	42	125
Total cash, cash equivalents and restricted cash at the end of the period	$ 32,776	$ 20,864	$ 24,060