Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue:
Product revenue	$ 7,269	$ 1,322
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember
Operating expenses:
Cost of product revenue	$ 3,072	$ 794
Type of Cost, Good or Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember
Research and development	$ 7,484	$ 5,516
Sales and marketing	5,871	3,438
General and administrative	3,001	1,376
Total operating expenses	19,428	11,124
Loss from operations	(12,159)	(9,802)
Interest expense	(245)	(18)
Change in fair value of warrant liability	(609)	41
Other income, net	221	185
Net loss before taxes	(12,792)	(9,594)
Income tax provision	7
Net loss	(12,799)	(9,594)
Unrealized gain on available-for-sale securities		1
Total comprehensive loss	$ (12,799)	$ (9,593)
Net loss per share, basic and diluted	$ (1.37)	$ (5.63)
Shares used in computing net loss per share, basic and diluted	9,364,755	1,705,144