Fair Value Measurements (Changes in the Fair Value of Real Estate Fund Investments and Deferred Compensation Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Real estate fund investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 462,132	$ 574,761
Dispositions/distributions	(91,606)	(71,888)
Net unrealized loss on held investments	(25,807)	(41,162)
Net realized gains on exited investments	36,078	14,761
Previously recorded unrealized gains on exited investments	(25,538)	(14,254)
Other, net	(455)	(86)
Ending balance	354,804	462,132
Deferred Compensation Plan Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	57,444	59,186
Purchases	5,786	5,355
Dispositions/distributions	(27,715)	(9,354)
Net unrealized loss on held investments	2,519	344
Net realized gains on exited investments	2,094	1,913
Ending balance	$ 40,128	$ 57,444