Consolidated Statement of Equity - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Par Value	Additional Paid in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	Total Shareholders’ Equity	Operating Partnership Noncontrolling Interest	Partially Owned Properties Noncontrolling Interest	Total Noncontrolling Interests
Balance at Dec. 31, 2017	$ 2,547,634	$ 1,814	$ 2,772,823	$ (315,417)	$ 13,952	$ 2,473,172	$ 73,844	$ 618	$ 74,462
Stockholders' Equity Attributable to Parent [Abstract]
Net proceeds from sale of common shares	5,970	3	5,967			5,970
Restricted share award grants, net	2,944	2	2,858	84		2,944
Purchase of OP Units	(303)						(303)		(303)
Conversion of OP Units	0	1	942			943	(943)		(943)
Dividends/distributions declared	(86,245)			(83,837)		(83,837)	(2,408)		(2,408)
Preferred distributions	(771)			(771)		(771)
Distributions	(86)							(86)	(86)
Change in market value of Redeemable Noncontrolling Interest	1,431		155	1,276		1,431
Change in fair value of interest rate swap agreements	5,619			0	5,619	5,619
Net income	23,232			22,495		22,495	644	93	737
Adjustment for Noncontrolling Interests ownership in Operating Partnership	0		(878)			(878)	878		878
Balance at Jun. 30, 2018	$ 2,499,425	$ 1,820	$ 2,781,867	$ (376,170)	$ 19,571	$ 2,427,088	$ 71,712	$ 625	$ 72,337