Financial Instruments - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Interest Rate Cap
Derivative [Line Items]
Notional amount	$ 1,200.0		$ 1,200.0
Cap agreement effective 12/31/18-12/31/20
Derivative [Line Items]
Notional amount	1,400.0		1,400.0
Premium payments on interest rate cap agreements			6.0
Interest Rate Contract
Derivative [Line Items]
Unrealized gain (loss) on effective portion of interest rate cap agreements	$ (4.0)		(12.0)
Unrealized gain (loss) on effective portion of interest rate cap agreements		$ 2.0		$ 5.0
Amount expected to be reclassified from AOCL to interest expense in next twelve months			(6.0)
Derivative
Derivative [Line Items]
Interest income (expense) reclassified into earnings (less than)		$ (1.0)	$ (2.0)	$ (2.0)