Commitments and Contingencies - Litigation and Related Contingencies (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Governmental Investigations
Litigation and Related Contingencies
Accruals for potential contingencies	$ 0.0	$ 0.0
Korea | Maximum
Litigation and Related Contingencies
Revenue percentage of total revenue	3.00%
Legal
Litigation and Related Contingencies
Accruals for potential contingencies	$ 0.0	$ 0.0