Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	$ 193,145	$ 203,704
Real estate fund investments	351,750	462,132
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	193,145	203,704
Real estate fund investments	351,750	462,132
Deferred compensation plan assets (included in restricted cash and other assets)	106,244	121,183
Interest rate swaps (included in other assets)	20,880	21,816
Total assets	672,019	808,835
Mandatorily redeemable instruments (included in other liabilities)	50,561	50,561
Interest rate swap (included in other liabilities)	3,090	10,122
Total liabilities	53,651	60,683
Recurring | Level 1
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	193,145	203,704
Real estate fund investments	0	0
Deferred compensation plan assets (included in restricted cash and other assets)	56,960	63,739
Interest rate swaps (included in other assets)	0	0
Total assets	250,105	267,443
Mandatorily redeemable instruments (included in other liabilities)	50,561	50,561
Interest rate swap (included in other liabilities)	0	0
Total liabilities	50,561	50,561
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)	20,880	21,816
Total assets	20,880	21,816
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (included in other liabilities)	3,090	10,122
Total liabilities	3,090	10,122
Recurring | Level 3
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	0	0
Real estate fund investments	351,750	462,132
Deferred compensation plan assets (included in restricted cash and other assets)	49,284	57,444
Interest rate swaps (included in other assets)	0	0
Total assets	401,034	519,576
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (included in other liabilities)	0	0
Total liabilities	0	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)	103,743	116,996
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)	$ 2,501	$ 4,187