Fair Value Measures - Fair Value, By Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instruments	$ 5,704,907	$ 5,957,640
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instruments	6,164,035	6,508,078
Level 2 [Member] | Mortgage Notes Payable and Other Debt, Net [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instruments	991,699	1,334,689
Level 2 [Member] | Mortgage Notes Payable and Other Debt, Net [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instruments	1,031,324	1,384,490
Level 2 [Member] | Corporate Bonds, Net [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instruments	4,625,208	4,622,951
Level 2 [Member] | Corporate Bonds, Net [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instruments	5,044,711	5,123,588
Level 2 [Member] | Credit Facility [Member] | Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instruments	88,000	0
Level 2 [Member] | Credit Facility [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instruments	$ 88,000	$ 0