Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	$ 188,695	$ 203,704
Real estate fund investments	454,946	462,132
Recurring
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	188,695	203,704
Real estate fund investments	454,946	462,132
Deferred compensation plan assets (included in other assets)	124,933	121,374
Interest rate swaps (included in other assets)	24,513	21,816
Total assets	793,087	809,026
Mandatorily redeemable instruments (included in other liabilities)	50,561	50,561
Interest rate swap (included in other liabilities)	7,221	10,122
Total liabilities	57,782	60,683
Recurring | Level 1
Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis
Marketable Securities	188,695	203,704
Real estate fund investments	0	0
Deferred compensation plan assets (included in other assets)	68,023	63,930
Interest rate swaps (included in other assets)	0	0
Total assets	256,718	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)	24,513	21,816
Total assets	24,513	21,816
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (included in other liabilities)	7,221	10,122
Total liabilities	7,221	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	454,946	462,132
Deferred compensation plan assets (included in other assets)	56,910	57,444
Interest rate swaps (included in other assets)	0	0
Total assets	511,856	519,576
Mandatorily redeemable instruments (included in other liabilities)	0	0
Interest rate swap (included in other liabilities)	0	0
Total liabilities	$ 0	$ 0