Fair Value of Instruments (Estimated Fair Value and Carrying Amounts) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of long-term debt	$ 11,236,731	$ 9,066,434
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of long-term debt	11,181,880	8,698,464
Global revolving credit facilities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred financing costs	15,400	7,200
Global revolving credit facilities | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lines of credit	1,663,156	558,191
Global revolving credit facilities | Carrying Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lines of credit	1,663,156	558,191
Unsecured term loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred financing costs	4,200	4,800
Unsecured term loan | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lines of credit	1,183,121	1,425,117
Unsecured term loan | Carrying Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Lines of credit	1,183,121	1,425,117
Unsecured senior notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of long-term debt	19,900	18,500
Deferred financing costs	$ 40,600	38,300
Unsecured senior notes | 5.875% notes due 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	5.875%
Unsecured senior notes | 3.400% notes due 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	3.40%
Unsecured senior notes | 3.950% notes due 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	3.95%
Unsecured senior notes | 3.625% notes due 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	3.625%
Unsecured senior notes | 4.750% notes due 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	4.75%
Unsecured senior notes | 2.750% notes due 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	2.75%
Unsecured senior notes | 2.625% notes due 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	2.625%
Unsecured senior notes | 2.750% notes due 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	2.75%
Unsecured senior notes | 4.750% notes due 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	4.75%
Unsecured senior notes | 4.250% notes due 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate	4.25%
Unsecured senior notes | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured senior notes	$ 7,684,368	6,976,603
Unsecured senior notes | Carrying Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured senior notes	7,629,679	6,608,545
Mortgage loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred financing costs	20,200	0
Mortgage loans | Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	706,086	106,523
Mortgage loans | Carrying Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Mortgage loans	$ 705,924	$ 106,611