Real Estate and Other Affiliates (Summary of Investments in Real Estate and Other Affiliates) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jul. 16, 2020	Jul. 15, 2020	Dec. 31, 2019
Investment in Real Estate and Other Affiliates
Carrying Value	$ 389,882		$ 389,882				$ 121,757
Share of Earnings/Dividends	266,838	$ 4,542	269,635	$ 20,847
Equity Method Investments
Investment in Real Estate and Other Affiliates
Carrying Value	385,929		385,929				117,804
Share of Earnings/Dividends	266,838	4,542	265,911	17,222
Other equity investments
Investment in Real Estate and Other Affiliates
Carrying Value	3,953		3,953				3,953
Share of Earnings/Dividends	0	0	3,724	3,625
110 North Wacker | Equity Method Investments
Investment in Real Estate and Other Affiliates
Carrying Value	273,600		273,600
Mr. C Seaport | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership						35.00%
Accounts payable and accrued expenses | The Metropolitan Downtown Columbia
Investment in Real Estate and Other Affiliates
Investment deficit position	$ 4,500		$ 4,500				$ 4,700
Operating Assets | 110 North Wacker | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	0.00%		0.00%				0.00%
Carrying Value	$ 273,608		$ 273,608
Operating Assets | The Metropolitan Downtown Columbia | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	50.00%		50.00%				50.00%
Carrying Value	$ 0		$ 0				$ 0
Share of Earnings/Dividends	$ 215	172	$ 637	478
Operating Assets | Stewart Title of Montgomery County, TX | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	50.00%		50.00%				50.00%
Carrying Value	$ 4,052		$ 4,052				$ 4,175
Share of Earnings/Dividends	$ 375	306	$ 878	579
Operating Assets | Woodlands Sarofim 1 | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	20.00%		20.00%				20.00%
Carrying Value	$ 3,091		$ 3,091				$ 2,985
Share of Earnings/Dividends	$ 32	38	$ 96	89
Operating Assets | m.flats/TEN.M | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	50.00%		50.00%				50.00%
Carrying Value	$ 1,820		$ 1,820				$ 2,431
Share of Earnings/Dividends	$ 340	(75)	$ 496	(1,576)
Master Planned Communities | The Summit | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	0.00%		0.00%				0.00%
Carrying Value	$ 85,327		$ 85,327				$ 84,455
Share of Earnings/Dividends	(1,563)	4,523	4,403	18,859
Seaport District | Mr. C Seaport | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership					0.00%		35.00%
Carrying Value	0		0				$ 7,650
Share of Earnings/Dividends	$ 0	(545)	$ (6,900)	(1,628)
Seaport District | Bar Wayo (Momofuku) | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	0.00%		0.00%				0.00%
Carrying Value	$ 6,963		$ 6,963				$ 7,469
Share of Earnings/Dividends	(288)	(160)	(2,064)	(160)
Strategic Developments | 110 North Wacker
Investment in Real Estate and Other Affiliates
Share of Earnings/Dividends	267,500		267,500
Strategic Developments | 110 North Wacker | Equity Method Investments
Investment in Real Estate and Other Affiliates
Share of Earnings/Dividends	$ 267,518		$ 267,518
Strategic Developments | Circle T Ranch and Power Center | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	50.00%		50.00%				50.00%
Carrying Value	$ 10,686		$ 10,686				$ 8,207
Share of Earnings/Dividends	$ 216	400	$ 891	691
Strategic Developments | HHMK Development | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	50.00%		50.00%				50.00%
Carrying Value	$ 10		$ 10				$ 10
Share of Earnings/Dividends	$ 0	0	$ 0	0
Strategic Developments | KR Holdings | Equity Method Investments
Investment in Real Estate and Other Affiliates
Economic/Legal Ownership	50.00%		50.00%				50.00%
Carrying Value	$ 372		$ 372				$ 422
Share of Earnings/Dividends	$ (7)	$ (117)	$ (44)	$ (110)