Quarterly Data (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue	$ 15,917,000	$ 14,944,000	$ 13,536,000	$ 12,337,000	$ 10,877,000	$ 10,591,000	$ 8,643,000	$ 7,521,000	$ 56,734,000	$ 37,632,000	$ 22,874,000
Cost of goods sold:
Total costs of goods sold and services	9,052,000	7,911,000	6,605,000	6,330,000	5,669,000	4,996,000	4,670,000	4,349,000	29,898,000	19,684,000	12,887,000
Gross profit	6,865,000	7,033,000	6,931,000	6,007,000	5,208,000	5,595,000	3,973,000	3,172,000	26,836,000	17,948,000	9,987,000
Operating expense:
Research and development	4,398,000	3,924,000	4,016,000	3,852,000	4,045,000	4,411,000	3,705,000	3,644,000	16,190,000	15,805,000	16,304,000
Selling, general and administrative	13,953,000	13,352,000	13,429,000	11,512,000	10,577,000	8,846,000	7,579,000	6,691,000	52,246,000	33,693,000	19,688,000
Total operating expenses	18,351,000	17,276,000	17,445,000	15,364,000	14,622,000	13,257,000	11,284,000	10,335,000	68,436,000	49,498,000
Loss from operations	(11,486,000)	(10,243,000)	(10,514,000)	(9,357,000)	(9,414,000)	(7,662,000)	(7,311,000)	(7,163,000)	(41,600,000)	(31,550,000)	(26,005,000)
Interest income (expense), net	282,000	282,000	42,000	21,000	24,000	30,000	16,000	(24,000)	627,000	46,000	(951,000)
Other income (expense), net	139,000	(34,000)	(68,000)	(47,000)	81,000	(25,000)	(48,000)	(15,000)	(10,000)	(7,000)	(63,000)
Income tax benefit (provision)	107,000	125,000	(23,000)	(22,000)	(25,000)				187,000	(25,000)	0
Net loss	$ (10,958,000)	$ (9,870,000)	$ (10,563,000)	$ (9,405,000)	$ (9,334,000)	$ (7,657,000)	$ (7,343,000)	$ (7,202,000)	$ (40,796,000)	$ (31,536,000)	$ (27,019,000)
Net loss per share, basic and diluted	$ (0.39)	$ (0.37)	$ (0.46)	$ (0.42)	$ (0.42)	$ (0.35)	$ (0.34)	$ (0.33)	$ (1.63)	$ (1.43)	$ (8.30)
Weighted-average common shares outstanding, basic and diluted	28,021,957	26,627,831	23,213,653	22,422,960	22,221,305	22,670,786	21,890,978	21,788,605	25,090,708	21,994,317	3,756,954
Product revenue
Revenue	$ 11,431,000	$ 10,737,000	$ 8,776,000	$ 9,547,000	$ 7,458,000	$ 5,962,000	$ 5,200,000	$ 4,745,000	$ 40,491,000	$ 23,365,000	$ 14,124,000
Cost of goods sold:
Total costs of goods sold and services	6,684,000	5,513,000	4,455,000	4,248,000	3,734,000	3,277,000	2,945,000	2,773,000	20,900,000	12,729,000	7,742,000
Service and other revenue
Revenue	4,302,000	4,207,000	4,760,000	2,790,000	3,419,000	3,017,000	3,174,000	2,507,000	16,059,000	12,117,000	7,676,000
Cost of goods sold:
Total costs of goods sold and services	2,368,000	$ 2,398,000	$ 2,150,000	$ 2,082,000	$ 1,935,000	1,719,000	1,725,000	1,576,000	8,998,000	6,955,000	5,145,000
Collaboration and license revenue
Revenue	$ 184,000					$ 1,612,000	$ 269,000	$ 269,000	$ 184,000	$ 2,150,000	$ 1,074,000