Geographical Data - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting [Abstract]
Material revenue attributable to individual foreign country	$ 0	$ 0	$ 0	$ 0
Long lived assets located in domestic markets	100.00%		100.00%		100.00%