Real Estate and Other Affiliates (Relevant Financial Information for the Summit) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) condominium_unit	Jun. 30, 2020 USD ($) condominium_unit	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Investments in and Advances to Affiliates [Line Items]
Total assets	$ 9,309,069		$ 9,309,069			$ 9,140,332
Total liabilities	5,610,385		5,610,385			5,396,195
Total equity	3,671,903	$ 3,739,703	3,671,903	$ 3,739,703	$ 3,661,267	3,715,023	$ 3,772,598	$ 3,332,988
Revenues	212,457	156,173	403,037	331,348
Operating income (loss)	25,659	(402)	(9,417)	(137,631)
Net income (loss)	3,617	$ (34,103)	(64,542)	(159,185)
The Summit
Investments in and Advances to Affiliates [Line Items]
Total assets	234,684		234,684			310,855
Total liabilities	180,597		180,597			209,968
Total equity	54,087		54,087			100,887
Revenues			199,505	58,672
Gross margin			69,695	10,256
Operating income (loss)			0	0
Net income (loss)			$ 69,372	$ 7,591
Number of units closed | condominium_unit			35	7
110 North Wacker
Investments in and Advances to Affiliates [Line Items]
Total assets	677,078		$ 677,078			634,274
Total liabilities	470,950		470,950			415,452
Total equity	$ 206,128		206,128			$ 218,822
Revenues			18,042	$ 0
Gross margin			0	0
Operating income (loss)			12,390	0
Net income (loss)			$ (16,777)	$ 0