CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 16,182	$ 13,381	$ 47,490	$ 39,756
Cost of goods sold	1,630	1,221	4,744	3,451
Gross profit	14,552	12,160	42,746	36,305
Operating expenses:
Sales and marketing	16,443	10,605	48,985	31,890
Research and development	1,874	1,373	5,503	3,875
General and administrative	6,816	3,226	15,776	8,198
Total operating expenses	25,133	15,204	70,264	43,963
Loss from operations	(10,581)	(3,044)	(27,518)	(7,658)
Interest and other income (expense), net:
Interest income	612	69	2,051	199
Interest expense	(1,243)	(1,282)	(3,706)	(3,826)
Other expense, net	(94)	(535)	(132)	(855)
Net loss	(11,306)	(4,792)	(29,305)	(12,140)
Other comprehensive income (loss):
Changes in foreign currency translation	(4)	(4)	(11)	29
Unrealized gain (loss) on marketable securities	(37)	0	47	0
Comprehensive loss	$ (11,347)	$ (4,796)	$ (29,269)	$ (12,111)
Net loss per share, basic and diluted (in dollars per share)	$ (0.46)	$ (1.29)	$ (1.19)	$ (3.34)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	24,803,452	3,712,876	24,596,788	3,638,905