CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenue	$ 16,317	$ 13,663	$ 31,308	$ 26,375
Cost of goods sold	1,588	1,182	3,114	2,230
Gross profit	14,729	12,481	28,194	24,145
Operating expenses:
Sales and marketing	16,727	10,318	32,542	21,285
Research and development	1,946	1,296	3,629	2,502
General and administrative	4,194	2,564	8,960	4,972
Total operating expenses	22,867	14,178	45,131	28,759
Loss from operations	(8,138)	(1,697)	(16,937)	(4,614)
Interest and other income (expense), net:
Interest income	695	68	1,439	130
Interest expense	(1,233)	(1,269)	(2,463)	(2,544)
Other expense, net	22	(249)	(38)	(320)
Net loss	(8,654)	(3,147)	(17,999)	(7,348)
Other comprehensive income (loss):
Changes in foreign currency translation	12	54	(7)	33
Unrealized gain on marketable securities	59	0	84	0
Comprehensive loss	$ (8,583)	$ (3,093)	$ (17,922)	$ (7,315)
Net loss per share, basic and diluted (in dollars per share)	$ (0.35)	$ (0.87)	$ (0.74)	$ (2.04)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	24,577,938	3,608,283	24,484,608	3,603,308