Share-based Compensation - Options (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of number of outstanding and exercisable options and the activity
Outstanding at beginning of year (in shares)	3,446,885	2,454,973
Exercisable at beginning of year (in shares)	1,643,011	1,137,766
Granted (in shares)	2,119,708	1,753,539
Exercised (in shares)	(36,040)	(832)
Expired, forfeited or cancelled (in shares)	(1,099,587)	(760,795)
Outstanding at end of period (in shares)	4,430,966	3,446,885	2,454,973
Exercisable at end of period (in shares)	1,518,972	1,643,011	1,137,766
Summary of weighted-average exercise price of outstanding and exercisable options and the activity
Outstanding at beginning of year (in dollars per share)	$ 8.935	$ 11.195
Exercisable at beginning of year (in dollars per share)	10.627	10.919
Granted (in dollars per share)	2.163	6.786
Exercised (in dollars per share)	0.320	0.320
Expired, forfeited or cancelled (in dollars per share)	9.816	11.281
Outstanding at end of period (in dollars per share)	5.551	8.935	$ 11.195
Exercisable at end of period (in dollars per share)	$ 8.735	$ 10.627	$ 10.919
Summary of intrinsic value of outstanding and exercisable options and other information
Intrinsic value, outstanding options	$ 53	$ 70	$ 4,764
Intrinsic value, exercisable options	$ 31	$ 70	$ 2,890
Weighted average remaining contractual life of options outstanding	8 years 2 months 12 days	7 years 10 months 24 days
Weighted-average remaining contractual life of options exercisable	6 years 10 months 24 days	6 years 7 months 6 days
Minimum
Summary of weighted-average exercise price of outstanding and exercisable options and the activity
Granted (in dollars per share)	$ 1.36	$ 4.76
Maximum
Summary of weighted-average exercise price of outstanding and exercisable options and the activity
Granted (in dollars per share)	$ 3.14	$ 10.40