Income per Common Share of the Trust (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income (Numerator) [Abstract]
Income from continuing operations net of noncontrolling interest	$ 91,331	$ 34,293	$ 157,797	$ 88,430
Discontinued operations net of noncontrolling interest	0	130	0	47,142
Net income available to common shareholders	$ 91,331	$ 34,423	$ 157,797	$ 135,572
Weighted Average Shares (Denominator) [Abstract]
Weighted Average Number of Shares Outstanding, Basic	148,582	147,422	148,594	146,987
Dilutive shares for long-term compensation plans	594	666	626	674
Weighted Average Number of Shares Outstanding, Diluted	149,176	148,088	149,220	147,661
Common shares [Member]
Earnings Per Share, Basic [Abstract]
Income from Continuing Operations, Per Basic Share	$ 0.61	$ 0.23	$ 1.06	$ 0.60
Income from Discontinued Operations, Per Basic Share	0.00	0.00	0.00	0.32
Income per common share - basic	0.61	0.23	1.06	0.92
Earnings Per Share, Diluted [Abstract]
Income from Continuing Operations, Per Diluted Share	0.61	0.23	1.06	0.60
Income from Discontinued Operations, Per Diluted Share	0.00	0.00	0.00	0.32
Income per common share - diluted	$ 0.61	$ 0.23	$ 1.06	$ 0.92