Related Party Transactions - Related Party Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Related party expenses, net	$ 12.1	$ 12.6	$ 16.9
Data entry, indexing services and other operating expenses
Related Party Transaction [Line Items]
Related party expenses, net	8.2	5.1	9.6
Corporate services
Related Party Transaction [Line Items]
Related party expenses, net	4.9	9.2	10.4
Technology and corporate services
Related Party Transaction [Line Items]
Related party expenses, net	$ 1.0	$ 1.7	$ 3.1