Stock Options, Restricted Stock Units and Employee Stock Purchase Plan - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Number of Options
Outstanding, beginning balance (in Shares)	3,418,000
Granted (in Shares)	860,000	0
Exercised (in Shares)	0
Forfeited (in Shares)	(196,000)
Outstanding, ending balance (in Shares)	4,082,000	3,418,000
Options, exercisable (in Shares)	2,599,000
Weighted Average Exercise Price
Outstanding, beginning balance (in Dollars per share)	$ 28.55
Granted (in Dollars per share)	3.90
Exercised (in Dollars per share)	0
Forfeited (in Dollars per share)	27.61
Outstanding, ending balance (in Dollars per share)	23.40	$ 28.55
Weighted average exercise price, exercisable (in Dollars per share)	$ 28.64
Weighted Average Remaining Contractual Term (Years)
Weighted Average Remaining Contractual Term	4 years 4 months 17 days	3 years 8 months 8 days
Weighted Average Remaining Contractual Term, exercisable	2 years 7 months 9 days
Aggregate Intrinsic Value (in thousands)
Aggregate Intrinsic Value	$ 0	$ 0
Aggregate Intrinsic Value, exercisable	$ 0