Financial Instruments - Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Liabilities:
Contingent consideration - other accrued liabilities and other long-term liabilities	$ 69.6	$ 73.9
Fair Value, Measurements, Recurring
Assets:
Total assets	100.1	97.7
Liabilities:
Interest rate swaps - other long-term liabilities	12.5
Contingent consideration - other accrued liabilities and other long-term liabilities	71.0	71.4
Total liabilities	83.5	71.4
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Assets:
Total assets	37.7	37.1
Liabilities:
Interest rate swaps - other long-term liabilities	0.0
Contingent consideration - other accrued liabilities and other long-term liabilities	0.0	0.0
Total liabilities	0.0	0.0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Total assets	62.4	60.6
Liabilities:
Interest rate swaps - other long-term liabilities	12.5
Contingent consideration - other accrued liabilities and other long-term liabilities	0.0	0.0
Total liabilities	12.5	0.0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Total assets	0.0	0.0
Liabilities:
Interest rate swaps - other long-term liabilities	0.0
Contingent consideration - other accrued liabilities and other long-term liabilities	71.0	71.4
Total liabilities	71.0	71.4
Fair Value, Measurements, Recurring | Interest Rate Swap
Assets:
Interest rate derivatives - other assets	5.9	2.5
Fair Value, Measurements, Recurring | Interest Rate Swap | Quoted Prices in Active Markets (Level 1)
Assets:
Interest rate derivatives - other assets	0.0	0.0
Fair Value, Measurements, Recurring | Interest Rate Swap | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives - other assets	5.9	2.5
Fair Value, Measurements, Recurring | Interest Rate Swap | Significant Unobservable Inputs (Level 3)
Assets:
Interest rate derivatives - other assets	0.0	0.0
Fair Value, Measurements, Recurring | Interest Rate Locks
Assets:
Interest rate derivatives - other assets	7.4	10.3
Fair Value, Measurements, Recurring | Interest Rate Locks | Quoted Prices in Active Markets (Level 1)
Assets:
Interest rate derivatives - other assets	0.0	0.0
Fair Value, Measurements, Recurring | Interest Rate Locks | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives - other assets	7.4	10.3
Fair Value, Measurements, Recurring | Interest Rate Locks | Significant Unobservable Inputs (Level 3)
Assets:
Interest rate derivatives - other assets	0.0	0.0
Carrying Amount
Assets:
Total assets	100.1	97.7
Liabilities:
Interest rate swaps - other long-term liabilities	12.5
Contingent consideration - other accrued liabilities and other long-term liabilities	71.0	71.4
Total liabilities	83.5	71.4
Carrying Amount | Interest Rate Swap
Assets:
Interest rate derivatives - other assets	5.9	2.5
Carrying Amount | Interest Rate Locks
Assets:
Interest rate derivatives - other assets	7.4	10.3
Money market mutual funds | Fair Value, Measurements, Recurring
Assets:
Money market mutual funds	37.7	37.1
Money market mutual funds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Assets:
Money market mutual funds	37.7	37.1
Money market mutual funds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Money market mutual funds	0.0	0.0
Money market mutual funds | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Money market mutual funds	0.0	0.0
Money market mutual funds | Carrying Amount
Assets:
Money market mutual funds	37.7	37.1
Bonds | Fair Value, Measurements, Recurring
Assets:
Bonds - restricted cash and marketable securities and other assets	49.1	47.8
Bonds | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)
Assets:
Bonds - restricted cash and marketable securities and other assets	0.0	0.0
Bonds | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Bonds - restricted cash and marketable securities and other assets	49.1	47.8
Bonds | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Bonds - restricted cash and marketable securities and other assets	0.0	0.0
Bonds | Carrying Amount
Assets:
Bonds - restricted cash and marketable securities and other assets	$ 49.1	$ 47.8