Fair Value Measurements (Changes in the Fair Value of Real Estate Fund Investments and Deferred Compensation Plan Assets) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Real estate fund investments
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 354,804	$ 462,132
Dispositions	(20,291)	0
Purchases	2,950	0
Net realized (loss) gain on exited investments	(911)	241
Net unrealized loss on held investments	0	(7,187)
Other, net	0	(240)
Ending balance	336,552	454,946
Deferred Compensation Plan Assets
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	40,128	57,444
Dispositions	(1,635)	(2,737)
Purchases	14	463
Realized and unrealized gains	678	1,075
Other, net	300	665
Ending balance	$ 39,485	$ 56,910