Tax Receivable Agreement - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Income Tax Contingency [Line Items]
Tax receivable agreement, percentage of income taxes	90.00%
Liability for tax receivable agreement	$ 135.8		$ 203.8
Other Operating Income (Expense)
Income Tax Contingency [Line Items]
Liability for tax receivable agreement	$ 68.0
Subsequent Event
Income Tax Contingency [Line Items]
Liability for tax receivable agreement		$ 15.9