Financial Instruments and Fair Value Measurements - Schedule of Other Financial Instruments Carrying Values and Fair values (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable	$ 101,450	$ 114,943	$ 111,775	$ 160,991
Mortgage and Other Notes Payable	1,763,839	1,708,196
Unsecured notes payable and Unsecured line of credit	500,083	477,320
Level 3 | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable	101,450	114,943
Mortgage and Other Notes Payable	1,131,315	1,179,503
Investment in non-traded equity securities	1,726	1,778
Level 3 | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable	102,135	113,422
Mortgage and Other Notes Payable	1,111,354	1,191,281
Investment in non-traded equity securities	1,456	57,964
Level 2 | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured notes payable and Unsecured line of credit	638,739	538,425
Level 2 | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured notes payable and Unsecured line of credit	$ 623,392	$ 539,362