Fair Value Measurements - Gains and Interest Expense on Interest Rate Swap Contracts (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gains recorded in accumulated other comprehensive loss, net of tax	$ (1.1)
Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Gains recorded in accumulated other comprehensive loss, net of tax	(2.6)	$ (2.8)
Interest expense recorded related to interest rate swap contracts	0.5	2.1
Interest rate swap | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Ineffectiveness recorded in interest expense	$ 0.0	$ 0.6