Consolidated Statement of Equity - 6 months ended Jun. 30, 2017 - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	AOCI Including Portion Attributable to Noncontrolling Interest	Parent	Operating Partnership Noncontrolling Interest	Partially Owned Properties Noncontrolling Interest	Noncontrolling Interest	Operating Partnership	Operating Partnership Partially Owned Properties Noncontrolling Interest
Balance at Dec. 31, 2016	$ 1,782,318	$ 1,360	$ 1,920,644	$ (197,261)	$ 13,708	$ 1,738,451	$ 43,142	$ 725	$ 43,867
Stockholders' Equity Attributable to Parent [Abstract]
Net proceeds from sale of common shares	383,676	214	383,462			383,676
Restricted share award grants, net	461	2	805	(346)		461
Purchase of OP Units	(3,757)						(3,757)		(3,757)
Conversion of OP Units			392			392	(392)		(392)
Dividends/distributions declared	(73,302)			(70,901)		(70,901)	(2,401)		(2,401)
Preferred distributions	(399)			(399)		(399)
Issuance of OP Units in connection with acquisitions	44,259						44,259		44,259
Contributions	47							47	47	$ 47	$ 47
Buyout of Noncontrolling Interests - partially owned properties	(2,105)		(2,800)			(2,800)	719	(24)	695	(2,105)	(24)
Distributions	(210)							(210)	(210)	(210)	(210)
Change in fair value of interest rate cap agreements	(780)				(780)	(780)				(780)
Net income	16,821			16,260		16,260	461	100	561	$ 16,821	$ 100
Adjustment for Noncontrolling Interests ownership in Operating Partnership			10,940			10,940	(10,940)		(10,940)
Balance at Jun. 30, 2017	$ 2,147,029	$ 1,576	$ 2,313,443	$ (252,647)	$ 12,928	$ 2,075,300	$ 71,091	$ 638	$ 71,729