Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	$ 157,951	$ 182,752
Real estate fund investments	369,767	354,804
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	157,951	182,752
Real estate fund investments	369,767	354,804
Deferred compensation plan assets (included in restricted cash and other assets)	102,281	109,177
Interest rate swaps (included in other assets)	40,203	27,472
Total assets	670,202	674,205
Mandatorily redeemable instruments (included in other liabilities)	50,561	520,561
Interest rate swap (included in other liabilities)		1,052
Total liabilities		521,613
Recurring | Level 1
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	157,951	182,752
Real estate fund investments	0	0
Deferred compensation plan assets (included in restricted cash and other assets)	63,493	69,049
Interest rate swaps (included in other assets)	0	0
Total assets	221,444	251,801
Mandatorily redeemable instruments (included in other liabilities)	50,561	520,561
Interest rate swap (included in other liabilities)		0
Total liabilities		520,561
Recurring | Level 2
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	0	0
Real estate fund investments	0	0
Deferred compensation plan assets (included in restricted cash and other assets)	0	0
Interest rate swaps (included in other assets)	40,203	27,472
Total assets	40,203	27,472
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (included in other liabilities)		1,052
Total liabilities		1,052
Recurring | Level 3
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	0	0
Real estate fund investments	369,767	354,804
Deferred compensation plan assets (included in restricted cash and other assets)	38,788	40,128
Interest rate swaps (included in other assets)	0	0
Total assets	408,555	394,932
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (included in other liabilities)		0
Total liabilities		0
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)	92,048	97,632
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)	$ 10,233	11,545
Other liabilities | Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Mandatorily redeemable instruments (included in other liabilities)		$ 50,561