Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 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	45,129	222,649
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities		33,313
Real estate fund investments	45,129	222,649
Deferred compensation plan assets (included in restricted cash and other assets)	90,888	103,773
Loans receivable (included in investments in partially owned entities and in other assets)	51,990
Interest rate swaps (included in other assets)	94	4,327
Total assets	188,101	364,062
Mandatorily redeemable instruments (included in other liabilities)	49,938	50,561
Interest rate swaps (included in other liabilities)	81,601	40,354
Total liabilities	131,539	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)	60,320	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	60,320	104,651
Mandatorily redeemable instruments (included in other liabilities)	49,938	50,561
Interest rate swaps (included in other liabilities)	0	0
Total liabilities	49,938	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)	94	4,327
Total assets	94	4,327
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	81,601	40,354
Total liabilities	81,601	40,354
Recurring | Level 3
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities		0
Real estate fund investments	45,129	222,649
Deferred compensation plan assets (included in restricted cash and other assets)	30,568	32,435
Loans receivable (included in investments in partially owned entities and in other assets)	51,990
Interest rate swaps (included in other assets)	0	0
Total assets	127,687	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)	12,116	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)	78,772	$ 91,954
Loans receivable (included in investments in partially owned entities and in other assets)	11,443
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)	$ 40,547