Income per Common Share of the Trust (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income Available to Common Stockholders, Basic [Abstract]
Income from continuing operations net of noncontrolling interest																	$ 170,471	$ 91,274	$ 88,008
Discontinued operations net of noncontrolling interest																	47,439	118,464	49,428
Net income available to common shareholders																	$ 217,910	$ 209,738	$ 137,436
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Weighted Average Number of Shares Outstanding, Basic																	147,216	130,180	116,863
Dilutive shares for long-term compensation plans																	670	729	831
Weighted Average Number of Shares Outstanding, Diluted																	147,886	130,909	117,694
Earnings Per Share, Basic [Abstract]
Income per common share - basic	$ 0.56	[1]	$ 0.23	[1]	$ 0.20	[1]	$ 0.49	[1]	$ 0.48	[1]	$ 0.21	[1]	$ 0.33	[1]	$ 0.60	[1]
Earnings Per Share, Diluted [Abstract]
Income per common share - diluted	$ 0.55	[1]	$ 0.23	[1]	$ 0.20	[1]	$ 0.49	[1]	$ 0.48	[1]	$ 0.21	[1]	$ 0.33	[1]	$ 0.60	[1]
Common shares [Member]
Earnings Per Share, Basic [Abstract]
Income from Continuing Operations, Per Basic Share																	$ 1.16	$ 0.70	$ 0.75
Income from Discontinued Operations, Per Basic Share																	$ 0.32	$ 0.91	$ 0.43
Income per common share - basic																	$ 1.48	$ 1.61	$ 1.18
Earnings Per Share, Diluted [Abstract]
Income from Continuing Operations, Per Diluted Share																	$ 1.15	$ 0.70	$ 0.75
Income from Discontinued Operations, Per Diluted Share																	$ 0.32	$ 0.90	$ 0.42
Income per common share - diluted																	$ 1.47	$ 1.60	$ 1.17

[1] The sum of quarterly financial data may vary from the annual data due to rounding.