Commitments and Contingencies (Narrative) (Details) $ in Thousands			3 Months Ended	12 Months Ended
	Feb. 24, 2018 USD ($)	Jan. 09, 2017 shareholder	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Lessee, Lease, Description [Line Items]
Option to extend, term			5 years
Rent expense			$ 900	$ 3,400	$ 3,400	$ 3,300
Variable lease cost			200
Lease liability, current			$ 1,700
Weighted-average remaining lease term			8 years 4 months 24 days
Weighted-average discount rate			22.20%
Settlement awarded to other party	$ 750
Number of shareholders in litigation | shareholder		2
Minimum
Lessee, Lease, Description [Line Items]
Term of contract			1 year
Severance payment, prior to change in control			6 months
Severance payment, period following change in control			18 months
Maximum
Lessee, Lease, Description [Line Items]
Term of contract			10 years
Severance payment, prior to change in control			18 months
Severance payment, period following change in control			24 months