Income per Common Share of the Trust (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income (Numerator) [Abstract]
Income from continuing operations net of noncontrolling interest	$ 12,123	$ 44,071	$ 56,953	$ 80,896
Income from discontinued operations net of noncontrolling interest	7,491	7,340	102,842	13,547
Net income available to common shareholders	$ 19,614	$ 51,411	$ 159,795	$ 94,443
Weighted Average Shares (Denominator) [Abstract]
Weighted Average Number of Shares or Units Outstanding, Basic	147,274	146,688	147,184	146,602
Dilutive shares for long-term compensation plans	1,059	820	920	753
Weighted Average Number of Shares or Units Outstanding, Diluted	148,333	147,508	148,104	147,355
Common shares [Member]
Earnings Per Share, Basic [Abstract]
Income from continuing operations	$ 0.08	$ 0.30	$ 0.39	$ 0.55
Income from discontinued operations	0.05	0.05	0.70	0.09
Income per common share or unit - basic	0.13	0.35	1.09	0.64
Earnings Per Share, Diluted [Abstract]
Income from continuing operations	0.08	0.30	0.39	0.55
Income from discontinued operations	0.05	0.05	0.69	0.09
Income per common share or unit - diluted	$ 0.13	$ 0.35	$ 1.08	$ 0.64