Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	$ 39,866	$ 152,198
Real estate fund investments	322,858	318,758
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	39,866	152,198
Real estate fund investments	322,858	318,758
Deferred compensation plan assets (included in restricted cash and other assets)	101,923	96,524
Interest rate swaps (included in other assets)	19,613	27,033
Total assets	484,260	594,513
Mandatorily redeemable instruments (included in other liabilities)	50,561	50,561
Interest rate swaps (included in other liabilities)	24,851	15,236
Total liabilities	75,412	65,797
Recurring | Level 1
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	39,866	152,198
Real estate fund investments	0	0
Deferred compensation plan assets (included in restricted cash and other assets)	64,361	58,716
Interest rate swaps (included in other assets)	0	0
Total assets	104,227	210,914
Mandatorily redeemable instruments (included in other liabilities)	50,561	50,561
Interest rate swaps (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)	19,613	27,033
Total assets	19,613	27,033
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swaps (included in other liabilities)	24,851	15,236
Total liabilities	24,851	15,236
Recurring | Level 3
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable securities	0	0
Real estate fund investments	322,858	318,758
Deferred compensation plan assets (included in restricted cash and other assets)	37,562	37,808
Interest rate swaps (included in other assets)	0	0
Total assets	360,420	356,566
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 (included in restricted cash and other assets)	93,176	88,122
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)	$ 8,747	$ 8,402