Stock Option Plan - Vested or Expected to Vest (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options outstanding and exercisable
Vested, Number of Shares (in shares)	2,210,969
Vested, Weighted Average Exercise Price (in dollars per share)	$ 11.66
Vested, Weighted Average Remaining Contractual Life	7 years 18 days
Vested, Aggregate Intrinsic Value	$ 977,587
Expected to vest, Number of Shares (in shares)	3,432,441
Expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 5.72
Expected to vest, Weighted Average Remaining Contractual Life	9 years 2 months 27 days
Expected to vest, Aggregate Intrinsic Value	$ 3,713,778
Fair value of common stock (in dollars per share)	$ 5.44
Aggregate intrinsic value of stock options exercised	$ 400	$ 1,100	$ 300
Fair value of options vested	$ 7,800	$ 7,100	$ 5,800