Long-Term Debt and Credit Facilities - Settlement Lines of Credit (Details) Kč in Millions, $ in Millions	Sep. 06, 2018 CZK (Kč)	Dec. 19, 2017 USD ($)	Dec. 01, 2017 USD ($)	Sep. 30, 2018 USD ($)	May 29, 2018 USD ($)	Dec. 31, 2017 USD ($)
Credit Facility | Deutsche Bank A.G.
Long-term debt
Maximum borrowing capacity			$ 35.0
Effective interest rate (as a percent)				6.75%
Borrowing capacity under the credit facility expressed as a percentage of eligible settlement receivables due			90.00%
Loan amounts drawn under the facility				$ 14.4		$ 12.6
Credit Facility | Wells Fargo Bank N.A.
Long-term debt
Maximum borrowing capacity		$ 10.0			$ 15.0
Effective interest rate (as a percent)				6.25%
Loan amounts drawn under the facility				$ 11.2		$ 9.9
Credit Facility | Prime rate | Deutsche Bank A.G.
Long-term debt
Basis spread on variable rate (as a percent)			1.50%
Credit Facility | Prime rate | Wells Fargo Bank N.A.
Long-term debt
Basis spread on variable rate (as a percent)		1.00%
Overdraft facility | PKO Bank
Long-term debt
Maximum borrowing capacity | Kč	Kč 100.0
Effective interest rate (as a percent)				2.87%
Loan amounts drawn under the facility				$ 0.1
Overdraft facility | Prague Interbank Offered Rate | PKO Bank
Long-term debt
Basis spread on variable rate (as a percent)	1.50%