Financing (Outstanding Financing Facilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 25, 2020	Dec. 31, 2019
Financing
Principal amount of long-term debt	$ 4,150,000		$ 3,911,000
Less: Unamortized discount and debt issuance costs	22,603		20,473
Long-term debt	4,127,397		3,890,527	[1]
4.875% Senior Notes due 2021 [Member]
Financing
Senior notes, principal amount	$ 500,000		$ 500,000
Interest rate of senior notes	4.875%		4.875%
Senior notes, effective interest rate	4.947%
4.625% Senior Notes due 2021 [Member]
Financing
Senior notes, principal amount	$ 300,000		$ 300,000
Interest rate of senior notes	4.625%		4.625%
Senior notes, effective interest rate	4.643%
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%
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%
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%
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%
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%
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%
4.200% Senior Notes due 2030 [Member]
Financing
Senior notes, principal amount	$ 500,000	$ 500,000
Interest rate of senior notes	4.20%	4.20%
Senior notes, effective interest rate	4.205%
Revolving Credit Facility [Member]
Financing
Unsecured revolving credit facility	$ 0		$ 261,000

[1] The balance sheet at December 31, 2019, has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by United States generally accepted accounting principles for complete financial statements.