Real Estate and Other Affiliates (Narrative) (Details) usdPerAcre in Thousands		3 Months Ended						6 Months Ended		9 Months Ended
	May 23, 2019 USD ($)	Jun. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2016	Mar. 31, 2015 USD ($) usdPerAcre	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 USD ($)
Investments in and Advances to Affiliates [Line Items]
Equity in earnings (losses) from real estate and other affiliates		$ 7,867,000		$ (8,552,000)				$ 23,663,000	$ 2,797,000
Equity Method Investments
Investments in and Advances to Affiliates [Line Items]
Equity method investment		294,209,000						294,209,000			$ 373,192,000
Equity in earnings (losses) from real estate and other affiliates		7,867,000		(8,552,000)				19,908,000	(927,000)
Other land, rental and property revenues
Investments in and Advances to Affiliates [Line Items]
Revenues from contracts with customers		$ 41,389,000		11,447,000				$ 64,632,000	46,344,000
HHC
Investments in and Advances to Affiliates [Line Items]
Equity method investment, ownership percentage		50.00%						50.00%
Discovery
Investments in and Advances to Affiliates [Line Items]
Equity method investment, ownership percentage		50.00%						50.00%
USAA Joint Venture
Investments in and Advances to Affiliates [Line Items]
Contribution of property					$ 33,600,000
Fair value of property contributed					$ 85,000,000.0
Capital contribution to joint venture										$ 9,800,000
Preferred return on capital					9.00%
Ownership interest								90.00%
USAA Joint Venture | Local Developer
Investments in and Advances to Affiliates [Line Items]
Capital contribution to joint venture					$ 5,000,000.0					$ 1,100,000
USAA Joint Venture | USAA
Investments in and Advances to Affiliates [Line Items]
Capital contribution to joint venture	$ 178,400,000				64,000,000.0
Joint venture capital obligations	$ 8,800,000				$ 105,600,000
Preferred return on capital					9.00%
Preferred return on capital of cash distribution					11.11%
Ownership interest								10.00%
110 North Wacker
Investments in and Advances to Affiliates [Line Items]
Equity method investment			$ 273,600,000
110 North Wacker | Strategic Developments Segment
Investments in and Advances to Affiliates [Line Items]
Equity in earnings (losses) from real estate and other affiliates			267,500,000
110 North Wacker | Strategic Developments Segment | Other land, rental and property revenues | Equity Method Investments
Investments in and Advances to Affiliates [Line Items]
Revenues from contracts with customers			$ 15,400,000
Ssäm Bar
Investments in and Advances to Affiliates [Line Items]
Preferred return on capital of cash distribution								75.00%
Joint venture real estate, percentage funded						89.75%
Preferred return on capital								10.00%
Join venture real estate, remaining cash distribution percentage								50.00%
Ssäm Bar | Momofuku
Investments in and Advances to Affiliates [Line Items]
Preferred return on capital of cash distribution								25.00%
Joint venture real estate, percentage funded						10.25%
Ssäm Bar | Seaport Segment | Equity Method Investments
Investments in and Advances to Affiliates [Line Items]
Equity method investment		$ 7,204,000						$ 7,204,000			$ 7,101,000
Equity in earnings (losses) from real estate and other affiliates		(336,000)		$ (384,000)				(688,000)	$ (1,776,000)
Investment in real estate and other affiliates		7,200,000						$ 7,200,000
The Summit
Investments in and Advances to Affiliates [Line Items]
Preferred return on capital								5.00%
Cash distribution entitlement by the joint venture								2
The Summit | Equity Method Investments
Investments in and Advances to Affiliates [Line Items]
Contribution of property							$ 13,400,000
SID bonds transferred to joint venture							1,300,000
Transaction value of land contributed to joint venture							$ 125,400,000	$ 125,400,000
Transactional value per acre of land contributed to joint venture | usdPerAcre							226
Maximum contribution required to joint venture by co-venturer							$ 30,000,000.0
Amount contributed on maximum contribution required to joint venture by co-venture							$ 3,750,000
110 North Wacker
Investments in and Advances to Affiliates [Line Items]
Recourse amount		100,600,000						100,600,000
Unconsolidated Properties
Investments in and Advances to Affiliates [Line Items]
Secured debt real estate affiliates		610,200,000						610,200,000
Share of entity in secured debt		$ 291,300,000						$ 291,300,000