REAL ESTATE AND OTHER AFFILIATES (Summarized Financial Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance Sheet
Total Assets	$ 9,140,332	$ 8,413,766
Total Liabilities	5,396,195	5,080,778
Total Equity	3,715,023	3,332,988	$ 3,238,126	$ 3,188,551
Income Statement
Revenues	699,489	1,300,539	1,064,537
Operating Income	(119,561)	150,310	106,806
Net income (loss)	(3,173)	74,295	57,726
The Summit
Balance Sheet
Total Assets	306,541	221,277
Total Liabilities	207,152	136,314
Total Equity	99,389	84,963
Income Statement
Revenues	147,680	120,337	102,559
Gross Margin	27,064	32,205	42,338
Net income (loss)	20,426	26,298	36,697
110 North Wacker
Balance Sheet
Total Assets	634,274	0
Total Liabilities	415,452	0
Total Equity	218,822	0
Income Statement
Revenues	5,333	0	0
Operating Income	(3,148)	0	0
Net income (loss)	(8,236)	0	0
Equity Method Investment, Nonconsolidated Investee, Other
Balance Sheet
Total Assets	247,742	324,926
Total Liabilities	166,418	208,991
Total Equity	81,324	115,935
Income Statement
Revenues	36,450	42,778	36,613
Operating Income	17,100	16,085	14,495
Net income (loss)	$ 11,220	$ 5,162	$ 6,250