Income per Common Share of the Trust Income per Common Share of the Trust (Computation of Basic and Diluted Income Per Common Share) (Details) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Income Per Common Share [Line Items]
Income from continuing operations net of noncontrolling interest	$ 30,535	$ 31,108	$ 89,993	$ 85,131
Weighted Average Number of Shares Outstanding, Diluted	115,780	113,773	115,329	113,388
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.27	$ 0.27	$ 0.78	$ 0.75
Dilutive shares for long-term compensation plans	766	696	782	680
Discontinued operations net of noncontrolling interest, Per Diluted Share	$ 0.04	$ 0.03	$ 0.51	$ 0.11
Net Income (Loss) Available to Common Stockholders, Basic	35,320	34,644	149,207	97,640
Weighted Average Number of Shares Outstanding, Basic	115,014	113,077	114,547	112,708
Earnings Per Share, Basic	$ 0.31	$ 0.31	$ 1.30	$ 0.87
Income (Loss) from Discontinued Operations, Net of Tax, Per Basic Share	$ 0.04	$ 0.03	$ 0.52	$ 0.11
Earnings Per Share, Diluted	$ 0.31	$ 0.30	$ 1.29	$ 0.86
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.27	$ 0.28	$ 0.78	$ 0.76
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ 4,785	$ 3,536	$ 59,214	$ 12,509