Commitments and Contingencies - Litigation and Related Contingencies (Details) - USD ($)	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Governmental Investigations
Litigation and Related Contingencies
Accruals for potential contingencies	$ 0	$ 0
Korea | Maximum
Litigation and Related Contingencies
Fine amount to be imposed	20,000
Legal
Litigation and Related Contingencies
Accruals for potential contingencies	$ 0	$ 0