Consolidated Statement of Equity Statement - 3 months ended Mar. 31, 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	301,572	173	301,399			301,572
Restricted share award grants, net	(1,146)	2	(943)	(205)		(1,146)
Purchase of OP Units	(3,725)						(3,725)		(3,725)
Conversion of OP Units			264			264	(264)		(264)
Dividends/distributions declared	(35,749)			(34,581)		(34,581)	(1,168)		(1,168)
Preferred distributions	(211)			(211)		(211)
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	(154)							(154)	(154)	(154)	(154)
Change in fair value of interest rate cap agreements	825				825	825				825
Net income	6,603			6,402		6,402	147	54	201	$ 6,603	$ 54
Adjustment for Noncontrolling Interests ownership in Operating Partnership			12,067			12,067	(12,067)		(12,067)
Balance at Mar. 31, 2017	$ 2,092,534	$ 1,535	$ 2,230,631	$ (225,856)	$ 14,533	$ 2,020,843	$ 71,043	$ 648	$ 71,691