Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Real estate fund investments	$ 3,739	$ 3,739
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Real estate fund investments	3,739	3,739
Deferred compensation plan assets (included in restricted cash and other assets)	107,238	105,564
Loans receivable (included in investments in partially owned entities and in other assets)	48,776	47,743
Interest rate swaps and caps (included in other assets)	4,994	17
Total assets	164,747	157,063
Mandatorily redeemable instruments (included in other liabilities)	50,267	50,002
Interest rate swaps (included in other liabilities)	50,818	66,033
Total liabilities	101,085	116,035
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)	62,383	65,636
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	62,383	65,636
Mandatorily redeemable instruments (included in other liabilities)	50,267	50,002
Interest rate swaps (included in other liabilities)	0	0
Total liabilities	50,267	50,002
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)	4,994	17
Total assets	4,994	17
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	50,818	66,033
Total liabilities	50,818	66,033
Recurring | Level 3
Financial Assets and Liabilities Measured at Fair Value on a Recurring and Nonrecurring Basis
Real estate fund investments	3,739	3,739
Deferred compensation plan assets (included in restricted cash and other assets)	44,855	39,928
Loans receivable (included in investments in partially owned entities and in other assets)	48,776	47,743
Interest rate swaps and caps (included in other assets)	0	0
Total assets	97,370	91,410
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	0	0
Total liabilities	0	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)	4,968	10,813
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)	102,270	94,751
Loans receivable (included in investments in partially owned entities and in other assets)	4,060	4,735
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)	$ 44,716	$ 43,008