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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Real estate fund investments
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 336,552	$ 454,946	$ 354,804	$ 462,132
Purchases	66,000	0	68,950	0
Net unrealized (loss) gain on held investments	(29,513)	745	(29,513)	(6,442)
Dispositions	0	0	(20,291)	0
Net realized (loss) gain on exited investments	(2)	0	(913)	241
Other, net	2	1	2	(239)
Ending balance	373,039	455,692	373,039	455,692
Deferred Compensation Plan Assets
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	39,485	56,910	40,128	57,444
Purchases	1,619	1,350	1,633	1,813
Sales	(1,874)	(9,375)	(3,509)	(12,112)
Realized and unrealized gains	34	830	712	1,905
Other, net	606	134	906	799
Ending balance	$ 39,870	$ 49,849	$ 39,870	$ 49,849