Income per Common Share of the Trust (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2010		Sep. 30, 2010		Jun. 30, 2010		Mar. 31, 2010		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Dilutive Shares, Shares Issued, Shares Acquired on Exchange [Abstract]
Common Units Exchanged																	119,987	82,621	63,613
Stock Issued During Period, Shares, Stock Options Exercised																	256,000	315,000	187,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount																	1,685,000	1,433,000	2,661,000
Income per Common Share of the Trust [Abstract]
Income from continuing operations net of noncontrolling interest																	$ 115,469	$ 105,172	$ 9,623
Weighted Average Shares, Diluted																	115,503,000	113,606,000	108,002,000
Income (Loss) from Continuing Operations, Per Diluted Share																	$ 1.00	$ 0.92	$ 0.09
Dilutive shares for long-term compensation plans																	748,000	682,000	452,000
Discontinued operations net of noncontrolling interest, Per Diluted Share																	$ 0.59	$ 0.20	$ 0.43
Net Income (Loss) Available to Common Stockholders, Basic																	183,999	127,762	56,376
Weighted Average Number of Shares Outstanding, Basic																	114,755,000	112,924,000	107,550,000
Earnings Per Share, Basic	$ 0.30	[1]	$ 0.31	[1]	$ 0.74	[1]	$ 0.25	[1]	$ 0.27	[1]	$ 0.31	[1]	$ 0.30	[1]	$ 0.26	[1]	$ 1.60	$ 1.13	$ 0.52
Income (Loss) from Discontinued Operations, Net of Tax, Per Basic Share																	$ 0.60	$ 0.20	$ 0.43
Earnings Per Share, Diluted	$ 0.30	[1]	$ 0.31	[1]	$ 0.74	[1]	$ 0.25	[1]	$ 0.26	[1]	$ 0.30	[1]	$ 0.29	[1]	$ 0.26	[1]	$ 1.59	$ 1.12	$ 0.52
Income (Loss) from Continuing Operations, Per Basic Share																	$ 1.00	$ 0.93	$ 0.09
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent																	$ 68,530	$ 22,590	$ 46,753

[1] The sum of quarterly financial data may vary from the annual data due to rounding.