Tax Receivable Agreement Liability (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Dec. 31, 2017	Jun. 30, 2018
Income Tax Contingency [Line Items]
Reduction in federal, state, local and non-US income taxes (in percentage)		90.00%
Liability for tax receivable agreement		$ 203.8
Gain in other income, net from tax items	$ 68.0
Liability for tax receivable agreement balance	135.8	135.8
Current Liability
Income Tax Contingency [Line Items]
Liability for tax receivable agreement	$ 15.9	$ 15.9