Income per Common Share of the Trust (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Dilutive Shares, Shares Issued, Shares Acquired on Exchange [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	953,000	965,000	925,000	1,119,000
Stock Issued During Period, Shares, Stock Options Exercised	162,000		511,000		256,000
Income per Common Share of the Trust [Abstract]
Income from continuing operations net of noncontrolling interest	$ 31,110	$ 32,717	$ 63,551	$ 57,513
Weighted Average Number of Shares Outstanding, Basic	116,683,000	114,623,000	116,359,000	114,285,000
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.26	$ 0.28	$ 0.54	$ 0.51
Dilutive shares for long-term compensation plans	876,000	783,000	806,000	802,000
Weighted Average Number of Shares Outstanding, Diluted	117,559,000	115,406,000	117,165,000	115,087,000
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.26	$ 0.28	$ 0.54	$ 0.50
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	3,001	52,261	7,649	56,374
Income (Loss) from Discontinued Operations, Net of Tax, Per Basic Share	$ 0.03	$ 0.46	$ 0.07	$ 0.49
Discontinued operations net of noncontrolling interest, Per Diluted Share	$ 0.03	$ 0.46	$ 0.07	$ 0.49
Net Income (Loss) Available to Common Stockholders, Basic	$ 34,111	$ 84,978	$ 71,200	$ 113,887
Earnings Per Share, Basic	$ 0.29	$ 0.74	$ 0.61	$ 1.00
Earnings Per Share, Diluted	$ 0.29	$ 0.74	$ 0.61	$ 0.99