Financing (Outstanding Financing Facilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	May 20, 2019	Dec. 31, 2018
Financing
Senior notes	$ 3,629,527		$ 3,130,122
Principal amount of long-term debt	3,911,000		3,437,000
Less: Unamortized discount and debt issuance costs	20,473		19,878
Senior notes, unamortized discount	3,500		4,300
Senior notes, unamortized debt issuance costs	18,000		17,100
Long-term debt	$ 3,890,527		3,417,122
Minimum [Member]
Financing
Interest rate of senior notes	3.55%
Maximum [Member]
Financing
Interest rate of senior notes	4.875%
Line of credit facility [Member]
Financing
Unsecured revolving credit facility	$ 261,000		287,000
Unsecured revolving credit facility, weighted-average variable interest rate	3.318%
Senior notes [Member] \| 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	4.949%
Senior notes [Member] \| 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	4.644%
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%	3.90%	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%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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