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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Dilutive Shares, Shares Issued, Shares Acquired on Exchange [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	625,000	953,000	773,000	925,000
Stock Issued During Period, Shares, Stock Options Exercised	120,000		477,000		841,000
Income per Common Share of the Trust [Abstract]
Income from continuing operations net of noncontrolling interest	$ 33,362	$ 29,449	$ 62,762	$ 60,786
Weighted Average Number of Shares Outstanding, Basic	120,081,000	116,683,000	119,416,000	116,359,000
Income from Continuing Operations, Per Basic Share	$ 0.27	$ 0.25	$ 0.53	$ 0.52
Dilutive shares for long-term compensation plans	830,000	876,000	813,000	806,000
Weighted Average Number of Shares Outstanding, Diluted	120,911,000	117,559,000	120,229,000	117,165,000
Income from Continuing Operations, Per Diluted Share	$ 0.27	$ 0.25	$ 0.53	$ 0.52
Income from Discontinued Operations, Net of Tax, Attributable to Parent	6,747	4,662	48,586	10,414
Income from Discontinued Operations, Net of Tax, Per Basic Share	$ 0.06	$ 0.04	$ 0.40	$ 0.09
Discontinued operations net of noncontrolling interest, Per Diluted Share	$ 0.06	$ 0.04	$ 0.40	$ 0.09
Net Income Available to Common Stockholders, Basic	$ 40,109	$ 34,111	$ 111,348	$ 71,200
Earnings Per Share, Basic	$ 0.33	$ 0.29	$ 0.93	$ 0.61
Earnings Per Share, Diluted	$ 0.33	$ 0.29	$ 0.93	$ 0.61