Share-based Compensation - Options (Details) - Stock options $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Summary of number of outstanding and exercisable options and the activity
Outstanding at beginning of year (in shares) | shares	3,446,885
Exercisable at beginning of year (in shares) | shares	1,643,011
Granted (in shares) | shares	2,082,958
Exercised (in shares) | shares	(36,040)
Expired, forfeited or cancelled (in shares) | shares	(946,006)
Outstanding at end of period (in shares) | shares	4,547,797	3,446,885
Exercisable at end of period (in shares) | shares	1,436,254	1,643,011
Summary of weighted-average exercise price of outstanding and exercisable options and the activity
Outstanding at beginning of year (in dollars per share)	$ 8.94
Exercisable at beginning of year (in dollars per share)	10.63
Granted (in dollars per share)	2.18
Exercised (in dollars per share)	0.32
Expired, forfeited or cancelled (in dollars per share)	10.34
Outstanding at end of period (in dollars per share)	5.62	$ 8.94
Exercisable at end of period (in dollars per share)	$ 9.18	$ 10.63
Summary of intrinsic value of outstanding and exercisable options and other information
Intrinsic value, outstanding options | $	$ 39	$ 70
Intrinsic value, exercisable options | $	$ 23	$ 70
Weighted average remaining contractual life of options outstanding	8 years 4 months 24 days	7 years 10 months 24 days
Weighted-average remaining contractual life of options exercisable	7 years	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