Long-Term Debt and Other Borrowing Arrangements - Carrying Values of Long-Term Debt and Other Borrowing Arrangements (Details) - USD ($)	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jul. 31, 2017	Oct. 31, 2016
Debt Instrument [Line Items]
Total senior subordinated notes	$ 1,485,900,000		$ 1,584,232,000
Less unamortized debt issuance costs	(22,700,000)		(23,484,000)
Long-term debt	1,463,200,000		1,560,748,000
Revolving credit agreement due 2022
Debt Instrument [Line Items]
Revolving credit agreement due 2022	$ 0		$ 0
3.875% Senior subordinated notes due 2028
Debt Instrument [Line Items]
Senior subordinated notes interest rate	3.875%		3.875%
Total senior subordinated notes	$ 400,050,000		$ 0
3.375% Senior subordinated notes due 2027
Debt Instrument [Line Items]
Senior subordinated notes interest rate	3.375%		3.375%
Total senior subordinated notes	$ 514,350,000		$ 540,810,000
4.125% Senior subordinated notes due 2026
Debt Instrument [Line Items]
Senior subordinated notes interest rate	4.125%		4.125%			4.125%
Total senior subordinated notes	$ 228,600,000		$ 240,360,000
2.875% Senior subordinated notes due 2025
Debt Instrument [Line Items]
Senior subordinated notes interest rate	2.875%		2.875%
Total senior subordinated notes	$ 342,900,000		$ 360,540,000
5.25% Senior subordinated notes due 2024
Debt Instrument [Line Items]
Senior subordinated notes interest rate	5.25%		5.25%
Total senior subordinated notes	$ 0		$ 200,000,000
5.50% Senior subordinated notes due 2023
Debt Instrument [Line Items]
Senior subordinated notes interest rate	5.50%		5.50%
Total senior subordinated notes	$ 0		$ 242,522,000
Senior Subordinated Notes
Debt Instrument [Line Items]
Total senior subordinated notes	$ 1,485,900,000
Senior Subordinated Notes | 3.875% Senior subordinated notes due 2028
Debt Instrument [Line Items]
Senior subordinated notes interest rate		3.875%
Senior Subordinated Notes | 3.375% Senior subordinated notes due 2027
Debt Instrument [Line Items]
Senior subordinated notes interest rate					3.375%
Senior Subordinated Notes | 2.875% Senior subordinated notes due 2025
Debt Instrument [Line Items]
Senior subordinated notes interest rate				2.875%
Senior Subordinated Notes | 5.25% Senior subordinated notes due 2024
Debt Instrument [Line Items]
Senior subordinated notes interest rate	5.25%
Senior Subordinated Notes | 5.50% Senior subordinated notes due 2023
Debt Instrument [Line Items]
Senior subordinated notes interest rate	5.50%