Stockholders' Equity and Stock-Based Compensation Expense - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 01, 2020	Jan. 01, 2019	Sep. 30, 2018	Mar. 31, 2020	Dec. 31, 2019
Employee Stock Purchase Plan
Stock-Based Compensation
Number of shares available for future issuance (in shares)			140,000	404,163
Percentage of annual increase to the total number of common stock outstanding (as a percent)			1.00%
Annual increase in the number of shares to the shares of common stock (in shares)	132,915	131,248	250,000
Maximum number of shares issued (in shares)				0
2015 and 2018 Stock Incentive Plan
Number of Options
Outstanding, as of beginning of period (in shares)	2,388,400			2,388,400
Granted (in shares)				839,200
Forfeited (in shares)				(11,100)
Outstanding, as of end of period (in shares)				3,216,500	2,388,400
Exercisable (in shares)				1,110,613
Weighted Average Exercise Price
Outstanding, as of beginning of period (in dollar per share)	$ 6.20			$ 6.20
Granted (in dollar per share)				4.87
Forfeited (in dollars per share)				5.01
Outstanding, as of end of period (in dollar per share)				5.86	$ 6.20
Exercisable (in dollar per share)				$ 5.66
Weighted Average Remaining Contractual Term (Years)
Options outstanding				8 years 6 months 29 days	8 years 5 months 9 days
Exercisable				7 years 6 months
Aggregate Intrinsic Value
Options outstanding					$ 906
Weighted average grant date fair value per share of options granted (in dollar per share)				$ 3.34