Income per Common Share of the Trust (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income (Numerator) [Abstract]
Income from continuing operations net of noncontrolling interest	$ 48,043	$ 40,204
Income from discontinued operations net of noncontrolling interest	92,138	2,828
Net income available to common shareholders	$ 140,181	$ 43,032
Weighted Average Shares (Denominator) [Abstract]
Weighted Average Number of Shares Outstanding, Basic	147,060	146,471
Dilutive shares for long-term compensation plans	813	750
Weighted Average Number of Shares Outstanding, Diluted	147,873	147,221
Common shares [Member]
Earnings Per Share, Basic [Abstract]
Income from continuing operations, per basic share	$ 0.33	$ 0.27
Income from discontinued operations, per basic share	0.62	0.02
Income per common share - basic	0.95	0.29
Earnings Per Share, Diluted [Abstract]
Income from continuing operations, per diluted share	0.33	0.27
Income from discontinued operations, per diluted share	0.62	0.02
Income per common share - diluted	$ 0.95	$ 0.29