Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities:
Net loss	$ (5,821)	$ (3,474)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	36	21
Change in fair value of convertible preferred stock warrant liability		(220)
Change in fair value of maturity date preferred stock warrant liability		(7)
Change in fair value of convertible shareholder notes derivative liability		139
Stock based compensation	1,298	58
Non-cash interest expense on convertible shareholder notes		1,107
Changes in operating assets and liabilities:
Accounts receivable	(68)	22
Inventory	(58)	18
Prepaid expenses	74	98
Accounts payable	60	185
Accrued expenses and other current liabilities, excluding accrued interest on convertible note	16	161
Deferred revenue	82	37
Deferred rent	12	(15)
Net cash used in operating activities	(4,369)	(1,870)
Investing activities:
Purchase of property and equipment	(100)
Purchase of short-term investments	(1,796)
Net cash used in investing activities	(1,896)
Financing activities:
Proceeds from the exercise of stock options	22
Net cash provided by financing activities	22
Net decrease in cash and cash equivalents	(6,243)	(1,870)
Cash and cash equivalents at beginning of period	21,352	3,557
Cash and cash equivalents at end of period	15,109	1,687
Supplemental disclosures for noncash investing activity:
Accounts payable recognized for the purchase of equipment	$ 5