Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 20,067	$ 17,026	$ 54,093	$ 44,721
Cost of goods sold	5,488	4,170	16,074	11,206
Gross profit	14,579	12,856	38,019	33,515
Operating expenses:
Research and development	4,711	3,187	11,232	9,008
Selling, general and administrative	19,202	17,064	54,652	45,064
Total operating expenses	23,913	20,251	65,884	54,072
Loss from operations	(9,334)	(7,395)	(27,865)	(20,557)
Interest income	249	565	951	1,215
Interest expense	(1,215)	(1,176)	(3,620)	(3,736)
Other income (expense), net	(15)	(1)	(74)	(21,046)
Net loss	(10,315)	(8,007)	(30,608)	(44,124)
Other comprehensive loss:
Unrealized gain (loss) on investments, net	(164)	0	150	0
Net change in other comprehensive loss	(164)	0	150	0
Net loss and comprehensive loss	$ (10,479)	$ (8,007)	$ (30,458)	$ (44,124)
Net loss per share, basic and diluted (in USD per share)	$ (0.31)	$ (0.26)	$ (0.94)	$ (2.18)
Weighted average common shares used to compute net loss per share, basic and diluted (in shares)	33,757,599	30,764,354	32,597,007	20,249,580