Common Stock, Common Stock Warrants and Stock Option Plan - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares
Outstanding, beginning of period (in shares)	1,929,391		1,865,415	1,560,453
Granted (in shares)		0	189,856	479,375
Exercised (in shares)	(299,737)		(112,647)	(112,965)
Cancelled (in shares)	(3,410)		(13,233)	(61,448)
Outstanding, end of period (in shares)	1,626,244		1,929,391	1,865,415	1,560,453
Weighted Average Exercise Price
Outstanding, beginning of period (in dollars per share)	$ 4.84		$ 4.63	$ 3.63
Granted (in dollars per share)			6.16	7.25
Exercised (in dollars per share)	3.91		3.36	2.48
Cancelled (in dollars per share)	6.94		6.53	3.65
Outstanding, end of period (in dollars per share)	$ 5.01		$ 4.84	$ 4.63	$ 3.63
Additional information
Weighted Average Remaining Contractual Term (Years)	6 years 10 months 24 days		6 years 10 months 24 days	7 years 7 months 6 days	7 years 7 months 6 days
Aggregate Intrinsic Value	$ 10,057		$ 7,146	$ 1,540	$ 4,632
Options vested and exercisable, end of period (in shares)	1,034,771
Options vested and exercisable, end of period (in dollars per share)	$ 4.42
Options vested and exercisable	6 years 3 months 18 days
Options vested and exercisable as of June 30, 2018	$ 7,002
Vested and expected to vest
Options vested and expected to vest, end of period (in shares)	1,582,822
Options vested and expected to vest, end of period (in dollars per share)	$ 4.97
Options vested and expected to vest	6 years 10 months 24 days
Options vested and expected to vest as of June 30, 2018	$ 9,849