Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Shares
Beginning balance - Outstanding (shares)	3,075,994	1,819,444
Granted (shares)	1,259,530	1,256,770
Exercised (shares)	0	0
Forfeited/expired (shares)	(282,611)	(220)
Ending balance - Outstanding (shares)	4,052,913	3,075,994	1,819,444
Exercisable (shares)	2,323,907	1,602,114
Vested or expected to vest (shares)	4,052,913	3,075,994
Weighted- Average Exercise Price
Beginning balance - Outstanding (in dollars per share)	$ 5.59	$ 7.52
Granted (in dollars per share)	1.73	2.80
Exercised (in dollars per share)	0	0
Forfeited/expired (in dollars per share)	5.81	9.64
Ending balance - Outstanding (in dollars per share)	4.37	5.59	$ 7.52
Exercisable (in dollars per share)	5.77	7.19
Vested or expected to vest (in dollars per share)	$ 4.37	$ 5.59
Weighted- Average Remaining Contractual Life (in years)
Balance - Outstanding	7 years 2 months 23 days	7 years 2 months 23 days	6 years 11 months 23 days
Exercisable	6 years 2 months 26 days	5 years 9 months 10 days
Vested or expected to vest	7 years 2 months 23 days	7 years 2 months 23 days
Aggregate Intrinsic Value ($000)
Balance - Outstanding	$ 0	$ 151	$ 32
Exercisable	0	15
Vested and expected to vest	$ 0	$ 151