Stockholders' Equity - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Shares
Exercised (in shares)	0
Aggregate Intrinsic Value
Exercised, aggregate intrinsic value	$ 0	$ 400,000	$ 1,300,000
Stock options
Shares
Outstanding beginning balance (in shares)	9,370,373
Granted (in shares)	3,651,400
Exercised (in shares)	0
Forfeited (in shares)	(1,517,165)
Expired/cancelled (in shares)	(106,393)
Outstanding ending balance (in shares)	11,398,215	9,370,373
Options exercisable at end of period (in shares)	5,848,562
Vested and expected to vest at end of period (in shares)	11,398,215
Weighted-Average Exercise Price
Outstanding beginning balance, weighted-average exercise price (in dollars per share)	$ 9.31
Granted, weighted-average exercise price (in dollars per share)	3.34
Exercised, weighted-average exercise price (in dollars per share)	0
Forfeited, weighted-average exercise price (in dollars per share)	7.70
Expired/cancelled, weighted-average exercise price (in dollars per share)	11.35
Outstanding ending balance, weighted-average exercise price (in dollars per share)	7.60	$ 9.31
Options exercisable at end of period, weighted-average exercise price (in dollars per share)	9.92
Vested and expected to vest at end of period, weighted-average exercise price ( in dollars per share)	$ 7.60
Weighted-Average Contractual Life (in years)
Outstanding balance, weighted-average contractual life (in years)	7 years 2 months 26 days
Options exercisable at end of period, weighted-average contractual life (in years)	5 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding beginning balance, aggregate intrinsic value	$ 387,596
Exercised, aggregate intrinsic value	0
Forfeited, aggregate intrinsic value	43,756
Outstanding ending balance, aggregate intrinsic value	267,830	$ 387,596
Options exercisable at end of period, aggregate intrinsic value	$ 267,440