Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Number of shares
Outstanding at beginning of period (in shares)	1,089,513
Granted (in shares)	244,000
Exercised (shares)	0
Forfeited (in shares)	0
Expired (in shares)	(822)
Outstanding at end of period (in shares)	1,332,691	1,089,513
Exercisable at end of period (in shares)	707,687
Weighted- average exercise price
Outstanding at beginning of period (in dollars per share)	$ 12.06
Granted (in dollars per share)	0.69
Exercised (in dollars per share)	0.00
Forfeited (in dollars per share)	0.00
Expired (in dollars per share)	6.24
Outstanding at end of period (in dollars per share)	9.98	$ 12.06
Exercisable at end of period (in dollars per share)	$ 16.74
Additional disclosures
Weighted-average remaining contractual term (in years), outstanding	7 years 6 months	7 years 3 months
Weighted-average remaining contractual term (in years), granted	9 years 10 months
Weighted-average remaining contractual term (in years), exercisable	6 years
Aggregate intrinsic value, outstanding	$ 0	$ 0
Aggregate intrinsic value, exercisable	$ 0