Stock-Based Compensation - Service Based Stock Options (Details) - Stock option awards - Service based awards - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Shares Underlying Options
Outstanding at the beginning of the period (in shares)	5,717,956	8,210,024
Granted (in shares)	1,947,162	2,288,386
Expired (in shares)	(1,408,709)	(4,249,596)
Forfeited (in shares)	(441,903)	(530,858)
Outstanding at the end of the period (in shares)	5,814,506	5,717,956	8,210,024
Exercisable at end of period (in shares)	2,612,079
Weighted Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 4.55	$ 7.06
Granted (in dollars per share)	0.88	1.94
Expired (in dollars per share)	(7.00)	(8.07)
Forfeited (in dollars per share)	(2.22)	(3.88)
Outstanding at the end of the period (in dollars per share)	2.91	$ 4.55	$ 7.06
Exercise price (in dollars per share)	$ 4.81
Weighted Average Remaining Contractual Term
Outstanding	7 years 6 months	6 years 7 months 6 days	5 years 1 month 6 days
Granted		9 years
Exercisable	5 years 8 months 12 days
Aggregate Intrinsic Value (in $1,000's)
Outstanding	$ 0	$ 0	$ 0
Granted		$ 0
Exercisable at end of period	$ 0