Summary of Significant Accounting Policies (Narrative) (Details)	6 Months Ended
	Jun. 30, 2018 USD ($) Segment	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment to accumulated deficit	$ (278,150,000)		$ (281,124,000)
ASC 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting segment | Segment	1
Percentage of service revenue that is recognized over a period of time against total revenue	5.00%
Deferred revenue	$ 19,000
ASC 606 [Member] | Difference Between Revenue Guidance in Effect Before and After Topic 606 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment to accumulated deficit		$ 0