Financial Instruments (Fair Value of Assets and Liabilities) (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Liabilities:
Contingent consideration - other long-term liabilities	$ 73,900,000	$ 71,300,000
Fuel Hedges
Assets:
Commodity hedges - other current assets	0	3,000,000.0
Liabilities:
Derivative liability	0
Fair Value
Assets:
Total assets	97,700,000	152,500,000
Liabilities:
Contingent consideration - other long-term liabilities	70,900,000	73,300,000
Total liabilities	70,900,000	73,500,000
Fair Value | Quoted Prices in Active Markets (Level 1)
Assets:
Total assets	37,100,000	30,300,000
Liabilities:
Contingent consideration - other long-term liabilities	0	0
Total liabilities	0	0
Fair Value | Significant Other Observable Inputs (Level 2)
Assets:
Total assets	60,600,000	122,200,000
Liabilities:
Contingent consideration - other long-term liabilities	0	0
Total liabilities	0	200,000
Fair Value | Significant Unobservable Inputs (Level 3)
Assets:
Total assets	0	0
Liabilities:
Contingent consideration - other long-term liabilities	70,900,000	73,300,000
Total liabilities	70,900,000	73,300,000
Fair Value | Fuel Hedges
Assets:
Hedge derivatives - other current assets		3,000,000.0
Fair Value | Fuel Hedges | Quoted Prices in Active Markets (Level 1)
Assets:
Hedge derivatives - other current assets		0
Fair Value | Fuel Hedges | Significant Other Observable Inputs (Level 2)
Assets:
Hedge derivatives - other current assets		3,000,000.0
Fair Value | Fuel Hedges | Significant Unobservable Inputs (Level 3)
Assets:
Hedge derivatives - other current assets		0
Fair Value | Interest Rate Swap
Assets:
Interest rate derivatives - other assets	2,500,000	8,000,000.0
Fair Value | Interest Rate Swap | Quoted Prices in Active Markets (Level 1)
Assets:
Interest rate derivatives - other assets	0	0
Fair Value | Interest Rate Swap | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives - other assets	2,500,000	8,000,000.0
Fair Value | Interest Rate Swap | Significant Unobservable Inputs (Level 3)
Assets:
Interest rate derivatives - other assets	0	0
Fair Value | Interest Rate Locks
Assets:
Interest rate derivatives - other assets	10,300,000	19,100,000
Fair Value | Interest Rate Locks | Quoted Prices in Active Markets (Level 1)
Assets:
Interest rate derivatives - other assets	0	0
Fair Value | Interest Rate Locks | Significant Other Observable Inputs (Level 2)
Assets:
Interest rate derivatives - other assets	10,300,000	19,100,000
Fair Value | Interest Rate Locks | Significant Unobservable Inputs (Level 3)
Assets:
Interest rate derivatives - other assets	0	0
Fair Value | Commodity hedges
Liabilities:
Derivative liability		200,000
Fair Value | Commodity hedges | Quoted Prices in Active Markets (Level 1)
Liabilities:
Derivative liability		0
Fair Value | Commodity hedges | Significant Other Observable Inputs (Level 2)
Assets:
Commodity hedges - other current assets	0
Liabilities:
Derivative liability	0	200,000
Fair Value | Commodity hedges | Significant Unobservable Inputs (Level 3)
Liabilities:
Derivative liability		0
Fair Value | Money market accounts
Assets:
Money market mutual funds	37,100,000	30,300,000
Fair Value | Money market accounts | Quoted Prices in Active Markets (Level 1)
Assets:
Money market mutual funds	37,100,000	30,300,000
Fair Value | Money market accounts | Significant Other Observable Inputs (Level 2)
Assets:
Money market mutual funds	0	0
Fair Value | Money market accounts | Significant Unobservable Inputs (Level 3)
Assets:
Money market mutual funds	0	0
Fair Value | Bonds
Assets:
Bonds - restricted cash and marketable securities and other assets	47,800,000	92,100,000
Fair Value | Bonds | Quoted Prices in Active Markets (Level 1)
Assets:
Bonds - restricted cash and marketable securities and other assets	0	0
Fair Value | Bonds | Significant Other Observable Inputs (Level 2)
Assets:
Bonds - restricted cash and marketable securities and other assets	47,800,000	92,100,000
Fair Value | Bonds | Significant Unobservable Inputs (Level 3)
Assets:
Bonds - restricted cash and marketable securities and other assets	0	0
Carrying Amount
Assets:
Total assets	97,700,000	152,500,000
Liabilities:
Contingent consideration - other long-term liabilities	70,900,000	73,300,000
Total liabilities	70,900,000	73,500,000
Carrying Amount | Fuel Hedges
Assets:
Hedge derivatives - other current assets		3,000,000.0
Carrying Amount | Interest Rate Swap
Assets:
Interest rate derivatives - other assets	2,500,000	8,000,000.0
Carrying Amount | Interest Rate Locks
Assets:
Interest rate derivatives - other assets	10,300,000	19,100,000
Carrying Amount | Commodity hedges
Liabilities:
Derivative liability		200,000
Carrying Amount | Money market accounts
Assets:
Money market mutual funds	37,100,000	30,300,000
Carrying Amount | Bonds
Assets:
Bonds - restricted cash and marketable securities and other assets	$ 47,800,000	$ 92,100,000