Financial Instruments and Fair Value Measurements - Schedule of Other Financial Instruments Carrying Values and Fair values (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable	$ 114,943	$ 111,775	$ 160,991	$ 283,125
Mortgage and Other Notes Payable	1,708,196	1,550,545
Unsecured notes payable and Unsecured line of credit	477,320	533,257
Level 3 | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable	114,943	111,775
Mortgage and Other Notes Payable	1,179,503	1,026,708
Investment in non-traded equity securities	1,778	0
Level 3 | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable	113,422	109,532
Mortgage and Other Notes Payable	1,191,281	1,021,075
Investment in non-traded equity securities	57,964	56,337
Level 2 | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured notes payable and Unsecured line of credit	538,425	533,625
Level 2 | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured notes payable and Unsecured line of credit	$ 539,362	$ 533,954