Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 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	17,453	222,649
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities		33,313
Real estate fund investments	17,453	222,649
Deferred compensation plan assets (included in restricted cash and other assets)	94,081	103,773
Loans receivable (included in investments in partially owned entities and in other assets)	46,675
Interest rate swaps (included in other assets)	67	4,327
Total assets	158,276	364,062
Mandatorily redeemable instruments (included in other liabilities)	50,058	50,561
Interest rate swaps (included in other liabilities)	81,502	40,354
Total liabilities	131,560	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)	57,909	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	57,909	104,651
Mandatorily redeemable instruments (included in other liabilities)	50,058	50,561
Interest rate swaps (included in other liabilities)	0	0
Total liabilities	50,058	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)	67	4,327
Total assets	67	4,327
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	81,502	40,354
Total liabilities	81,502	40,354
Recurring | Level 3
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities		0
Real estate fund investments	17,453	222,649
Deferred compensation plan assets (included in restricted cash and other assets)	36,172	32,435
Loans receivable (included in investments in partially owned entities and in other assets)	46,675
Interest rate swaps (included in other assets)	0	0
Total assets	100,300	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)	12,444	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)	81,637	$ 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)	$ 41,430