Basis of Presentation and Summary of Significant Accounting Policies - Revenue, Derivatives, etc. (Details) - USD ($) $ in Millions		12 Months Ended
	Jul. 01, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basis of Presentation and Summary of Significant Accounting Policies
Payment term extended to associate VAR		30 days
Deferred taxes provided for basis difference in foreign subsidiaries		$ 0.0
Treasury shares cancelled, shares	7,310,022
Treasury shares cancelled, value	$ 106.5
Vendors payable term (in days)		30 days
Merchant payables term (in days)		20 days
Selling, General and Administrative Expenses
Basis of Presentation and Summary of Significant Accounting Policies
Advertising expense		$ 5.0	$ 5.0	$ 5.4