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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Real estate fund investments
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 373,039	$ 455,692	$ 354,804	$ 462,132
Net unrealized loss on held investments	(3,283)	(11,220)	(32,796)	(28,860)
Dispositions	0	(91,606)	(20,291)	(91,606)
Previously recorded unrealized gain on exited investment	0	(36,736)	0	(25,538)
Net realized gain (loss) on exited investments	0	35,620	(913)	35,861
Purchases / additional fundings	0	0	68,950	0
Other, net	11	0	13	(239)
Ending balance	369,767	351,750	369,767	351,750
Deferred Compensation Plan Assets
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	39,870	49,849	40,128	57,444
Sales	(3,304)	(3,810)	(6,813)	(15,922)
Realized and unrealized gains	180	246	892	2,151
Purchases / additional fundings	1,576	2,176	3,209	3,989
Other, net	466	823	1,372	1,622
Ending balance	$ 38,788	$ 49,284	$ 38,788	$ 49,284