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Financing (Outstanding Financing Facilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Oct. 14, 2020	Sep. 23, 2020	Mar. 27, 2020	Dec. 31, 2019
Financing
Total principal amount of debt	$ 4,150,000				$ 3,911,000
Less: Unamortized discount and debt issuance costs	26,783				20,473
Senior notes, unamortized discount	5,100				3,500
Senior notes, unamortized debt issuance costs	22,300				18,000
Total long-term debt	4,123,217				3,890,527
4.875% Senior Notes due 2021 [Member]
Financing
Senior notes, principal amount		$ 500,000
4.200% Senior Notes due 2030 [Member]
Financing
Senior notes, principal amount				$ 500,000
Interest rate of senior notes				4.20%
1.750% Senior Notes due 2031 [Member]
Financing
Senior notes, principal amount			$ 500,000
Interest rate of senior notes			1.75%
Revolving Credit Facility [Member]
Financing
Unsecured revolving credit facility	0				261,000
Senior notes [Member]
Financing
Senior notes, principal amount	4,200,000
Senior notes [Member] \| 4.875% Senior Notes due 2021 [Member]
Financing
Senior notes, principal amount	$ 0				$ 500,000
Interest rate of senior notes					4.875%
Senior notes [Member] \| 4.625% Senior Notes due 2021 [Member]
Financing
Interest rate of senior notes	4.625%				4.625%
Senior notes, effective interest rate	4.643%
Senior notes [Member] \| 3.800% Senior Notes due 2022 [Member]
Financing
Senior notes, principal amount	$ 300,000				$ 300,000
Interest rate of senior notes	3.80%				3.80%
Senior notes, effective interest rate	3.845%
Senior notes [Member] \| 3.850% Senior Notes due 2023 [Member]
Financing
Senior notes, principal amount	$ 300,000				$ 300,000
Interest rate of senior notes	3.85%				3.85%
Senior notes, effective interest rate	3.851%
Senior notes [Member] \| 3.550% Senior Notes due 2026 [Member]
Financing
Senior notes, principal amount	$ 500,000				$ 500,000
Interest rate of senior notes	3.55%				3.55%
Senior notes, effective interest rate	3.57%
Senior notes [Member] \| 3.600% Senior Notes due 2027 [Member]
Financing
Senior notes, principal amount	$ 750,000				$ 750,000
Interest rate of senior notes	3.60%				3.60%
Senior notes, effective interest rate	3.619%
Senior notes [Member] \| 4.350% Senior Notes due 2028 [Member]
Financing
Senior notes, principal amount	$ 500,000				$ 500,000
Interest rate of senior notes	4.35%				4.35%
Senior notes, effective interest rate	4.383%
Senior notes [Member] \| 3.900% Senior Notes due 2029 [Member]
Financing
Senior notes, principal amount	$ 500,000				$ 500,000
Interest rate of senior notes	3.90%				3.90%
Senior notes, effective interest rate	3.901%
Senior notes [Member] \| 4.200% Senior Notes due 2030 [Member]
Financing
Senior notes, principal amount	$ 500,000				$ 0
Interest rate of senior notes	4.20%
Senior notes, effective interest rate	4.205%
Senior notes [Member] \| 1.750% Senior Notes due 2031 [Member]
Financing
Senior notes, principal amount	$ 500,000				$ 0
Interest rate of senior notes	1.75%
Senior notes, effective interest rate	1.798%