Debt (Interest Rate Derivatives) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018	Mar. 27, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative, Term of Contract	3 years
OCI cash flow hedge gain (loss) before reclassification	$ 26,700,000
OCI cash flow hedge gain (loss) reclassification	2,200,000
OCI cash flow hedge gain (loss) after reclassification	24,500,000
Interest expense	100,300,000	$ 49,500,000	$ 57,600,000
Interest Rate Derivatives
Derivative Instruments and Hedging Activities Disclosures [Line Items]
OCI cash flow hedge gain (loss) before reclassification	26,700,000
OCI cash flow hedge gain (loss) after reclassification	24,500,000
Interest expense	8,600,000
Senior Notes
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Aggregate principal amount					$ 900,000,000.0
Floating rate senior notes due March 2021 | Senior Notes
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Aggregate principal amount	$ 300,000,000.0				$ 300,000,000.0
Floating rate senior notes due March 2021 | Senior Notes | Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Aggregate principal amount				$ 150,000,000.0
State interest rate				2.72%