Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	$ 187,489	$ 203,704
Real estate fund investments	455,692	462,132
Restricted cash	86,386	98,295	$ 94,628	$ 107,799
Other assets	644,922	515,437
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	187,489	203,704
Real estate fund investments	455,692	462,132
Deferred compensation plan assets (included in other assets)	104,566	121,374
Interest rate swaps (included in other assets)	20,998	21,816
Total assets	768,745	809,026
Mandatorily redeemable instruments (included in other liabilities)	50,561	50,561
Interest rate swap (included in other liabilities)	5,011	10,122
Total liabilities	55,572	60,683
Restricted cash	2,691	4,187
Other assets	101,875	117,187
Recurring | Level 1
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	187,489	203,704
Real estate fund investments	0	0
Deferred compensation plan assets (included in other assets)	54,717	63,930
Interest rate swaps (included in other assets)	0	0
Total assets	242,206	267,634
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 other assets)	0	0
Interest rate swaps (included in other assets)	20,998	21,816
Total assets	20,998	21,816
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (included in other liabilities)	5,011	10,122
Total liabilities	5,011	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	455,692	462,132
Deferred compensation plan assets (included in other assets)	49,849	57,444
Interest rate swaps (included in other assets)	0	0
Total assets	505,541	519,576
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (included in other liabilities)	0	0
Total liabilities	$ 0	$ 0