Earnings per Share ("EPS"): (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Numerator
Income from continuing operations	$ 17,986		$ 91,418		$ 37,629		$ 111,389
Income from discontinued operations	0		143,398		0		145,956
Net income attributable to noncontrolling interests	(1,898)		(15,819)		(3,722)		(20,256)
Net income attributable to the Company	16,088		218,997		33,907		237,089
Allocation of earnings to participating securities	(120)		(217)		(248)		(216)
Numerator for basic earnings per share—net income attributable to common stockholders	15,968		218,780		33,659		236,873
Numerator for diluted earnings per share-net income (loss) available to common stockholders	$ 15,968		$ 218,780		$ 33,659		$ 236,873
Denominator (in shares)
Denominator for basic earnings per share—weighted average number of common shares outstanding	140,894		139,372		140,831		138,460
Effect of dilutive securities:
Share and unit-based compensation plans	142	[1]	154	[1]	98	[1]	121	[1]
Denominator for diluted earnings per share—weighted average number of common shares outstanding	141,036	[1]	139,526	[1]	140,929	[1]	138,581	[1]
Earnings per common share—basic: (in dollars per share)
Income from continuing operations	$ 0.11		$ 0.61		$ 0.24		$ 0.73
Discontinued operations	$ 0.00		$ 0.96		$ 0.00		$ 0.98
Net income attributable to common stockholders	$ 0.11		$ 1.57		$ 0.24		$ 1.71
Earnings per common share—diluted: (in dollars per share)
Income from continuing operations	$ 0.11		$ 0.61		$ 0.24		$ 0.73
Discontinued operations	$ 0.00		$ 0.96		$ 0.00		$ 0.98
Net income attributable to common stockholders	$ 0.11		$ 1.57		$ 0.24		$ 1.71

[1] Diluted EPS excludes 184,304 convertible preferred units for the three and six months ended June 30, 2014 and 2013 as their impact was antidilutive.Diluted EPS excludes 10,113,486 and 9,938,795 Operating Partnership units ("OP Units") for the three months ended June 30, 2014 and 2013, respectively, and 10,052,805 and 10,072,120 OP Units for the six months ended June 30, 2014 and 2013, respectively, as their impact was antidilutive.