Debt Narrative (Details) - USD ($)				1 Months Ended				12 Months Ended
	Feb. 02, 2018	Jan. 31, 2018	Dec. 16, 2015	Sep. 30, 2017	Aug. 31, 2017	Mar. 31, 2016	Nov. 30, 2010	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Loss on extinguishment of debt								$ 10,100,000	$ 0	$ 0
Short-term debt								68,100,000	3,200,000
Commercial paper								63,000,000	0
Line of credit outstanding, current portion								5,100,000	3,200,000
Interest and fees paid								47,900,000	37,100,000	29,500,000
Make whole payment for extinguishment of debt								300,000,000	0	$ 0
Other LOC
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity								53,900,000	51,400,000
Line of credit outstanding, current portion								$ 21,500,000	$ 21,000,000
Notes 2022 Term Interest Rate Lock
Debt Instrument [Line Items]
Loss on forward interest rate lock, recorded in accumulated other comprehensive loss							$ 1,600,000
Senior Notes | Notes 2027 Term
Debt Instrument [Line Items]
Face amount					$ 300,000,000
Interest rate, stated percentage					3.15%			3.15%
Proceeds from debt, net of issuance costs					$ 294,600,000
Senior Notes | Notes 2018 Term
Debt Instrument [Line Items]
Interest rate, stated percentage				5.95%					5.95%
Debt instrument, repurchase amount				$ 300,000,000
Loss on extinguishment of debt				$ 10,100,000
Make whole payment for extinguishment of debt								$ 9,900,000
Senior Notes | Notes 2026 Term
Debt Instrument [Line Items]
Face amount						$ 400,000,000
Interest rate, stated percentage						3.35%		3.35%	3.35%
Proceeds from issuance of long-term debt						$ 393,400,000
Senior Notes | Notes 2022 Term
Debt Instrument [Line Items]
Face amount							$ 300,000,000
Interest rate, stated percentage							3.625%	3.625%	3.625%
Senior Notes | Notes 2028 Term | Subsequent Event
Debt Instrument [Line Items]
Face amount	$ 450,000,000
Interest rate, stated percentage	3.50%
Proceeds from issuance of long-term debt	$ 442,600,000
Line of Credit | Term Loan Agreement | Subsequent Event
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity	$ 500,000,000	$ 500,000,000
Amortization percentage, equal quarterly installments, year one	5.00%
Amortization percentage, equal quarterly installments, year two	5.00%
Amortization percentage, equal quarterly installments, year three	7.50%
Amortization percentage, equal quarterly installments, year four	10.00%
Amortization percentage, equal quarterly installments, year five	10.00%
Line of Credit | Revolving Credit Facility | Credit Agreement
Debt Instrument [Line Items]
Debt instrument, term			5 years
Line of credit, maximum borrowing capacity			$ 750,000,000
Line of credit facility, accordion feature, higher borrowing capacity option			$ 1,250,000,000.000
Line of credit facility covenants maximum debt to capitalization percentage			55.00%
Line of Credit | Revolving Credit Facility | Credit Agreement | Subsequent Event
Debt Instrument [Line Items]
Debt instrument, term		5 years
Line of credit, maximum borrowing capacity		$ 750,000,000
Line of credit facility, accordion feature, higher borrowing capacity option		$ 1,250,000,000.000
Line of credit facility covenants maximum debt to capitalization percentage		65.00%