Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (31,536)	$ (27,019)	$ (23,173)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	1,352	482	444
Stock-based compensation expense	4,884	2,168	928
Non-cash interest expense	170	238	388
Gain on disposal of fixed assets	(14)		11
Non-cash research and development expense for issuance of warrants to a vendor			2,078
Change in fair value of preferred stock warrants		90	307
Changes in operating assets and liabilities:
Accounts receivable	(983)	(1,682)	(1,655)
Deposits			200
Prepaid expenses and other assets	(1,828)	(273)	6
Inventory	(1,603)	(2,043)	(526)
Other non-current assets	267
Accounts payable	1,318	1,003	1,131
Accrued compensation and benefits, other accrued expenses and other liabilities	1,101	2,035	1,200
Deferred revenue	(1,849)	2,895	919
Net cash used in operating activities	(28,721)	(22,106)	(17,742)
Investing activities
Purchases of property and equipment	(1,518)	(1,132)	(526)
Acquisitions, net of cash acquired	(3,801)		(300)
Purchase of investments	(150)
Proceeds from sale of assets	15
Net cash used in investing activities	(5,454)	(1,132)	(826)
Financing activities
Proceeds from sale of preferred stock, net of issuance costs		65,575
Proceeds from sale of common stock, net of issuance costs	(20)	8,423	45,428
Proceeds from exercise of stock warrants		29	18
Proceeds from stock options exercised	1,871	202	213
Proceeds from the issuance of notes payable and warrants, net of issuance costs		(59)	2,954
Payments on notes payable	(1,929)	(921)	(2,697)
Net cash (used in) provided by financing activities	(78)	73,249	45,916
Net decrease in cash and cash equivalents	(34,253)	50,011	27,348
Cash, restricted cash, and cash equivalents at beginning of period	79,682	29,671	2,323
Cash, restricted cash, and cash equivalents at end of period	45,429	79,682	29,671
Supplemental cash flow information
Accretion of redeemable convertible preferred stock to redemption value		4,110	4,437
Cash paid for interest	660	743	945
Warrants issued to lenders		119	128
Purchases of property and equipment included in accounts payable	78	74	72
Fair value of common stock warrants exercised and reclassified as shares of common stock	$ 196	$ 2,187	$ 5,257