Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	$ 149,766	$ 182,752
Real estate fund investments	336,552	354,804
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	149,766	182,752
Real estate fund investments	336,552	354,804
Deferred compensation plan assets (included in restricted cash and other assets)	109,525	109,178
Interest rate swaps (included in other assets)	36,678	27,472
Total assets	632,521	674,206
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	149,766	182,752
Real estate fund investments	0	0
Deferred compensation plan assets (included in restricted cash and other assets)	70,040	69,050
Interest rate swaps (included in other assets)	0	0
Total assets	219,806	251,802
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)	36,678	27,472
Total assets	36,678	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	336,552	354,804
Deferred compensation plan assets (included in restricted cash and other assets)	39,485	40,128
Interest rate swaps (included in other assets)	0	0
Total assets	376,037	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)	98,133	97,633
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)	$ 11,392	$ 11,545