Fair Value Measurements (Details 1) (USD $) In Thousands, unless otherwise specified			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Real Estate Funds [Member] Investments	Mar. 31, 2012 Real Estate Funds [Member]	Mar. 31, 2013 Real Estate Funds [Member] Minimum [Member]	Mar. 31, 2013 Real Estate Funds [Member] Maximum [Member]	Mar. 31, 2013 Real Estate Funds [Member] Weighted Average [Member]	Mar. 31, 2013 Deferred Compensation Plan Asset [Member]	Mar. 31, 2012 Deferred Compensation Plan Asset [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Number Of Investments Made By Fund			9
Real Estate Fund Nondepreciable Real Estate	$ 571,306	$ 600,786	$ 571,306
Excess of fair value over cost			81,158
Fair Value Inputs Holding Period					1 year 3 months 20 days	7 years 3 months 20 days
Unobservable Quantitative Input [Abstract]
Discount rates					12.50%	19.00%	14.40%
Terminal capitalization rates					5.30%	6.30%	5.80%
Beginning Balance			600,786	346,650				62,631	56,221
Purchases			13,668	0				2,707	3,611
Sales			(56,664)	(31,052)				(2,697)	(3,395)
Unrealized gains			13,516	6,844
Realized and unrealized gains								1,354	2,392
Other, Net			0	2,072				1,015	52
Ending Balance			$ 571,306	$ 324,514				$ 65,010	$ 58,881