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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income (Numerator) [Abstract]
Income from continuing operations net of noncontrolling interest	$ 48,595	$ 56,487	$ 104,885	$ 136,460
Income from discontinued operations net of noncontrolling interest	101,548	3,052	205,053	17,522
Net income available to common shareholders	$ 150,143	$ 59,539	$ 309,938	$ 153,982
Weighted Average Shares (Denominator) [Abstract]
Weighted Average Number of Shares or Units Outstanding, Basic	147,324	146,811	147,241	146,678
Dilutive shares for long-term compensation plans	947	785	919	752
Weighted Average Number of Shares or Units Outstanding, Diluted	148,271	147,596	148,160	147,430
Common shares [Member]
Earnings Per Share, Basic [Abstract]
Income from continuing operations	$ 0.33	$ 0.39	$ 0.71	$ 0.93
Income from discontinued operations	0.69	0.02	1.39	0.12
Income per common share or unit - basic	1.02	0.41	2.10	1.05
Earnings Per Share, Diluted [Abstract]
Income from continuing operations	0.33	0.38	0.71	0.92
Income from discontinued operations	0.68	0.02	1.38	0.12
Income per common share or unit - diluted	$ 1.01	$ 0.40	$ 2.09	$ 1.04