Financial Instruments and Fair Value Measurements - Fair Value by Balance Sheet Grouping (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes receivable, net	$ 250,194	$ 276,163
Mortgage and Other Notes Payable, net	1,602,847	1,488,718
Unsecured notes payable and Unsecured line of credit, net	497,970	432,990
Carrying Amount | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes receivable, net	250,194	276,163
Mortgage and Other Notes Payable, net	1,060,550	1,071,034
Investment in non-traded equity securities (b)	0	802
Carrying Amount | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured notes payable and Unsecured line of credit, net	558,620	434,636
Estimated Fair Value | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes receivable, net	247,143	272,052
Mortgage and Other Notes Payable, net	1,066,539	1,077,926
Investment in non-traded equity securities (b)	22,904	25,194
Estimated Fair Value | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unsecured notes payable and Unsecured line of credit, net	$ 559,978	$ 435,779