Earnings per Share ("EPS"): (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator
Net income	$ 36,314	$ 38,744	$ 78,727	$ 76,373
Net income attributable to noncontrolling interests	(2,717)	(2,830)	(6,124)	(6,552)
Net income attributable to the Company	33,597	35,914	72,603	69,821
Allocation of earnings to participating securities	(147)	(122)	(442)	(373)
Numerator for basic and diluted earnings per share—net income attributable to common stockholders	$ 33,450	$ 35,792	$ 72,161	$ 69,448
Denominator
Denominator for basic earnings per share—weighted average number of common shares outstanding (in shares)	158,517	140,916	158,452	140,859
Effect of dilutive securities:
Share and unit-based compensation plans (in shares)	117	144	151	116
Denominator for diluted earnings per share—weighted average number of common shares outstanding (in shares)	158,634	141,060	158,603	140,975
Earnings per common share—net income attributable to common stockholders:
Basic (in dollars per share)	$ 0.21	$ 0.25	$ 0.46	$ 0.49
Diluted (in dollars per share)	$ 0.21	$ 0.25	$ 0.45	$ 0.49