Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	$ 152,198	$ 182,752
Real estate fund investments	318,758	354,804
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	152,198	182,752
Real estate fund investments	318,758	354,804
Deferred compensation plan assets ($8,402 included in restricted cash and $88,122 in other assets)	96,524	109,177
Interest rate swaps (included in other assets)	27,033	27,472
Total assets	594,513	674,205
Mandatorily redeemable instruments (included in other liabilities)	50,561	520,561
Interest rate swaps (included in other liabilities)	15,236	1,052
Total liabilities	65,797	521,613
Recurring | Level 1
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	152,198	182,752
Real estate fund investments	0	0
Deferred compensation plan assets ($8,402 included in restricted cash and $88,122 in other assets)	58,716	69,049
Interest rate swaps (included in other assets)	0	0
Total assets	210,914	251,801
Mandatorily redeemable instruments (included in other liabilities)	50,561	520,561
Interest rate swaps (included in other liabilities)	0	0
Total liabilities	50,561	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 ($8,402 included in restricted cash and $88,122 in other assets)	0	0
Interest rate swaps (included in other assets)	27,033	27,472
Total assets	27,033	27,472
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	15,236	1,052
Total liabilities	15,236	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	318,758	354,804
Deferred compensation plan assets ($8,402 included in restricted cash and $88,122 in other assets)	37,808	40,128
Interest rate swaps (included in other assets)	0	0
Total assets	356,566	394,932
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (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 ($8,402 included in restricted cash and $88,122 in other assets)	88,122	97,632
Restricted Cash | Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Deferred compensation plan assets ($8,402 included in restricted cash and $88,122 in other assets)	$ 8,402	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