Equity - Shares and Units and Dividends (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Class of Stock [Line Items]
Net income attributable to common stockholders	$ 11,220	$ 8,322	$ 25,478	$ 22,525
Change from net income attributable to common stockholders and transfers from noncontrolling interests	$ 35,648		$ 78,491
Shares and Units [Abstract]
OP units outstanding (shares)	267,579,408		267,579,408
OP units owned by the Company (shares)	117,954,034		117,954,034
OP units owned by the Company, percent			44.10%
OP units not owned by the Company (shares)	149,625,374		149,625,374
OP units not owned by the Company, percent			55.90%
Dividends and Distributions [Abstract]
Dividends paid to common shareholders	$ 10,000	8,300	$ 29,000	24,600
Distributions paid to OP unitholders	12,800	14,400	39,200	39,900
Private perpetual preferred unit distributions	200	$ 200	702	$ 241
Additional Paid-In Capital
Class of Stock [Line Items]
Increase in additional paid-in capital for the conversion of OP Units into common stock	$ 24,428		$ 53,013