Income per Common Share of the Trust (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Dilutive Shares, Shares Issued, Shares Acquired on Exchange [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	992,000	1,384,000
Stock Issued During Period, Shares, Stock Options Exercised	357,000		841,000
Income per Common Share of the Trust [Abstract]
Income from continuing operations net of noncontrolling interest	$ 29,925	$ 31,872
Weighted Average Number of Shares Outstanding, Basic	118,688,000	115,972,000
Income from Continuing Operations, Per Basic Share	$ 0.25	$ 0.28
Dilutive shares for long-term compensation plans	844,000	771,000
Weighted Average Number of Shares Outstanding, Diluted	119,532,000	116,743,000
Income from Continuing Operations, Per Diluted Share	$ 0.25	$ 0.28
Income from Discontinued Operations, Net of Tax, Attributable to Parent	41,314	5,217
Income from Discontinued Operations, Net of Tax, Per Basic Share	$ 0.35	$ 0.04
Discontinued operations net of noncontrolling interest, Per Diluted Share	$ 0.35	$ 0.04
Net Income Available to Common Stockholders, Basic	$ 71,239	$ 37,089
Earnings Per Share, Basic	$ 0.60	$ 0.32
Earnings Per Share, Diluted	$ 0.60	$ 0.32