STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 50,593	$ 28,567	$ 16,427
Cost of goods sold	10,056	6,018	3,905
Gross profit	40,537	22,549	12,522
Operating expenses:
Research and development	7,388	6,194	7,091
Selling, general and administrative	53,527	32,358	22,684
Total operating expenses	60,915	38,552	29,775
Operating loss	(20,378)	(16,003)	(17,253)
Other expense (income):
Interest income	(1,870)	(203)	(57)
Interest expense	3,304	1,753	1,303
Other expense (income), net	16	(42)	29
Total other expense	1,450	1,508	1,275
Loss before income taxes	(21,828)	(17,511)	(18,528)
Income taxes	0	0	0
Net loss	(21,828)	(17,511)	(18,528)
Unrealized losses on short-term investments	(52)	0	0
Total comprehensive loss	$ (21,880)	$ (17,511)	$ (18,528)
Net loss per share, basic and diluted (in dollars per share)	$ (1.50)	$ (14.88)	$ (16.90)
Weighted average common shares used to compute net loss per share, basic and diluted (in shares)	14,579,662	1,176,650	1,096,013