Equity - Shares and Units and Dividends (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Class of Stock [Line Items]
Net income attributable to common stockholders	$ 11,120	$ 9,834	$ 14,258	$ 14,203
Change from net income attributable to common stockholders and transfers from noncontrolling interests	$ 20,213		$ 42,844
Shares and Units [Abstract]
OP units outstanding (shares)	267,586,424		267,586,424
OP units owned by the Company (shares)	114,253,886		114,253,886
OP units owned by the Company, percent			42.70%
OP units not owned by the Company (shares)	153,332,538		153,332,538
OP units not owned by the Company, percent			57.30%
Dividends and Distributions [Abstract]
Dividends paid to common shareholders	$ 9,700	8,100	$ 19,100	16,300
Distributions paid to OP unitholders	13,100	$ 12,800	26,400	25,600
Private perpetual preferred unit distributions	200		468	$ 0
Additional Paid-in Capital
Class of Stock [Line Items]
Increase in additional paid-in capital for the conversion of OP units into common stock	$ 9,093		$ 28,586