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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share, Basic and Diluted [Line Items]
Document Period End Date			Jun. 30, 2019
Income (Numerator) [Abstract]
Income from continuing operations net of noncontrolling interest	$ 52,764	$ 7,308	$ 92,000	$ 47,447
Income from discontinued operations net of noncontrolling interest	47,005	12,306	62,100	112,348
Net income available to common shareholders	$ 99,769	$ 19,614	$ 154,100	$ 159,795
Weighted Average Shares (Denominator) [Abstract]
Income from continuing operations net of noncontrolling interest - basic, weighted average shares (in shares)	147,805	147,274	147,706	147,184
Dilutive shares for long-term compensation plans, weighted average shares (in shares)	863	1,059	900	920
Income from continuing operations net of noncontrolling interest - diluted, weighted average shares (in shares)	148,668	148,333	148,606	148,104
Common shares
Earnings Per Share, Basic [Abstract]
Income from continuing operations (in usd per share)	$ 0.36	$ 0.05	$ 0.62	$ 0.33
Income from discontinued operations (in usd per share)	0.32	0.08	0.42	0.76
Income per common share or unit - basic (in usd per share)	0.68	0.13	1.04	1.09
Earnings Per Share, Diluted [Abstract]
Income from continuing operations (in usd per share)	0.35	0.05	0.62	0.32
Income from discontinued operations (in usd per share)	0.32	0.08	0.42	0.76
Income per common share or unit - diluted (in usd per share)	$ 0.67	$ 0.13	$ 1.04	$ 1.08