Share-based Compensation - Options (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of number of outstanding and exercisable options and the activity
Outstanding at beginning of year (in shares)	2,454,973	2,107,344	1,352,283
Exercisable at beginning of year (in shares)	1,137,766	595,424	229,000
Granted (in shares)	1,753,539	570,432	859,257
Exercised (in shares)	(832)	(1,249)	(10,886)
Expired, forfeited or cancelled (in shares)	(760,795)	(221,554)	(93,310)
Outstanding at end of period (in shares)	3,446,885	2,454,973	2,107,344
Exercisable at end of period (in shares)	1,643,011	1,137,766	595,424
Summary of weighted-average exercise price of outstanding and exercisable options and the activity
Outstanding at beginning of year (in dollars per share)	$ 11.195	$ 12.173	$ 13.607
Exercisable at beginning of year (in dollars per share)	10.919	9.715	3.385
Exercise price (in dollars per share)	6.786	7.220	10.385
Exercised (in dollars per share)	0.320	0.223	1.231
Expired, forfeited or cancelled (in dollars per share)	11.281	10.325	17.780
Outstanding at end of period (in dollars per share)	8.935	11.195	12.173
Exercisable at end of period (in dollars per share)	$ 10.627	$ 10.919	$ 9.715
Summary of intrinsic value of outstanding and exercisable options and other information
Intrinsic value, outstanding options	$ 70	$ 4,764	$ 1,128	$ 964
Intrinsic value, exercisable options	$ 70	$ 2,890	$ 881	$ 2,504
Weighted average remaining contractual life of options outstanding	7 years 10 months 24 days
Weighted-average remaining contractual life of options exercisable	6 years 7 months 6 days
Minimum
Summary of weighted-average exercise price of outstanding and exercisable options and the activity
Exercise price (in dollars per share)	$ 4.76
Maximum
Summary of weighted-average exercise price of outstanding and exercisable options and the activity
Exercise price (in dollars per share)	$ 10.40