Financial Instruments and Fair Value Measurements - Schedule of Other Financial Instruments Carrying Values and Fair values (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable	$ 109,769	$ 109,613
Mortgage and Other Notes Payable	1,599,179	1,550,545
Unsecured notes payable and Unsecured line of credit	481,019	533,257
Level 3 | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable	109,769	109,613
Mortgage and Other Notes Payable	1,120,349	1,026,708
Investment in non-traded equity securities	0	0
Level 3 | Estimated Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Receivable	108,343	107,370
Mortgage and Other Notes Payable	1,122,067	1,021,075
Investment in non-traded equity securities	23,208	23,208
Level 2 | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured notes payable and Unsecured line of credit	490,425	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	$ 490,819	$ 533,954