Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	$ 0	$ 33,313
Real estate fund investments	3,739	222,649
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities		33,313
Real estate fund investments	3,739	222,649
Deferred compensation plan assets (included in restricted cash and other assets)	98,543	103,773
Loans receivable (included in investments in partially owned entities and in other assets)	47,509
Interest rate swaps (included in other assets)	17	4,327
Total assets	149,808	364,062
Mandatorily redeemable instruments (included in other liabilities)	49,947	50,561
Interest rate swaps (included in other liabilities)	73,536	40,354
Total liabilities	123,483	90,915
Recurring | Level 1
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities		33,313
Real estate fund investments	0	0
Deferred compensation plan assets (included in restricted cash and other assets)	59,597	71,338
Loans receivable (included in investments in partially owned entities and in other assets)	0
Interest rate swaps (included in other assets)	0	0
Total assets	59,597	104,651
Mandatorily redeemable instruments (included in other liabilities)	49,947	50,561
Interest rate swaps (included in other liabilities)	0	0
Total liabilities	49,947	50,561
Recurring | Level 2
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities		0
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
Interest rate swaps (included in other assets)	17	4,327
Total assets	17	4,327
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	73,536	40,354
Total liabilities	73,536	40,354
Recurring | Level 3
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities		0
Real estate fund investments	3,739	222,649
Deferred compensation plan assets (included in restricted cash and other assets)	38,946	32,435
Loans receivable (included in investments in partially owned entities and in other assets)	47,509
Interest rate swaps (included in other assets)	0	0
Total assets	90,194	255,084
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 Basis
Deferred compensation plan assets (included in restricted cash and other assets)	9,703	11,819
Other Assets | Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Deferred compensation plan assets (included in restricted cash and other assets)	88,840	$ 91,954
Loans receivable (included in investments in partially owned entities and in other assets)	5,335
Investments in Partially Owned Properties | Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Loans receivable (included in investments in partially owned entities and in other assets)	$ 42,174