Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Real estate fund investments	$ 13,402		$ 7,730
Payments to acquire short-term investments	645,920	$ 0
Investments in U.S. Treasury bills	645,360		0
US Treasury Bill Securities
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Payments to acquire short-term investments	645,920
Investments in U.S. Treasury bills	650,000
Amortized cost, current	646,049
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Real estate fund investments	13,402		7,730
Deferred compensation plan assets (included in restricted cash and other assets)	107,170		110,174
Loans receivable (included in investments in partially owned entities and in other assets)	50,848		50,182
Interest rate swaps and caps (included in other assets)	59,739		18,929
Total assets	876,519		187,015
Mandatorily redeemable instruments (included in other liabilities)	49,775		49,659
Interest rate swaps (included in other liabilities)	7,737		32,837
Total liabilities	57,512		82,496
Recurring | US Treasury Bill Securities
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Investments in U.S. Treasury bills	645,360
Recurring | Level 1
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Real estate fund investments	0		0
Deferred compensation plan assets (included in restricted cash and other assets)	62,644		65,158
Loans receivable (included in investments in partially owned entities and in other assets)	0		0
Interest rate swaps and caps (included in other assets)	0		0
Total assets	708,004		65,158
Mandatorily redeemable instruments (included in other liabilities)	49,775		49,659
Interest rate swaps (included in other liabilities)	0		0
Total liabilities	49,775		49,659
Recurring | Level 1 | US Treasury Bill Securities
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Investments in U.S. Treasury bills	645,360
Recurring | Level 2
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Real estate fund investments	0		0
Deferred compensation plan assets (included in restricted cash and other assets)	0		0
Loans receivable (included in investments in partially owned entities and in other assets)	0		0
Interest rate swaps and caps (included in other assets)	59,739		18,929
Total assets	59,739		18,929
Mandatorily redeemable instruments (included in other liabilities)	0		0
Interest rate swaps (included in other liabilities)	7,737		32,837
Total liabilities	7,737		32,837
Recurring | Level 2 | US Treasury Bill Securities
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Investments in U.S. Treasury bills	0
Recurring | Level 3
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Real estate fund investments	13,402		7,730
Deferred compensation plan assets (included in restricted cash and other assets)	44,526		45,016
Loans receivable (included in investments in partially owned entities and in other assets)	50,848		50,182
Interest rate swaps and caps (included in other assets)	0		0
Total assets	108,776		102,928
Mandatorily redeemable instruments (included in other liabilities)	0		0
Interest rate swaps (included in other liabilities)	0		0
Total liabilities	0		0
Recurring | Level 3 | US Treasury Bill Securities
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Investments in U.S. Treasury bills	0
Restricted Cash | Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Deferred compensation plan assets (included in restricted cash and other assets)	9,084		9,104
Other Assets | Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Deferred compensation plan assets (included in restricted cash and other assets)	98,086		101,070
Loans receivable (included in investments in partially owned entities and in other assets)	3,476		3,738
Investments in Partially Owned Properties | Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Loans receivable (included in investments in partially owned entities and in other assets)	$ 47,372		$ 46,444