Commitments and Contingencies (Narrative) (Details) $ in Millions		3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 09, 2017 shareholder	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	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		$ 0.9	$ 1.7	$ 3.4	$ 3.4	$ 3.3
Variable lease cost		0.3	0.5
Lease liability, current		$ 1.7	$ 1.7
Weighted-average remaining lease term		8 years 2 months 24 days	8 years 2 months 24 days
Weighted-average discount rate		22.10%	22.10%
Number of shareholders in litigation | shareholder	2
Minimum
Lessee, Lease, Description [Line Items]
Term of contract		1 year	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	10 years
Severance payment, prior to change in control			18 months
Severance payment, period following change in control			24 months