Consolidated Statement of Equity - 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net proceeds from sale of common shares	5,316	3	5,313			5,316
Restricted share award grants, net	933	2	872	59		933
Conversion of OP Units	0	0	126			126	(126)		(126)
Dividends/distributions declared	(43,126)		0	(41,910)		(41,910)	(1,216)		(1,216)
Preferred distributions	(487)			(487)		(487)	0		0
Distributions	(43)							(43)	(43)
Change in market value of Redeemable Noncontrolling Interest	1,470		194	1,276		1,470		0	0
Change in fair value of interest rate swap agreements	4,298				4,298	4,298		0
Net income	11,265			10,908		10,908	313	44	357
Adjustment for Noncontrolling Interests ownership in Operating Partnership	0		(712)			(712)	712		712
Balance at Mar. 31, 2018	2,527,260	1,819	2,778,616	(345,571)	18,250	2,453,114	73,527	619	74,146
Balance at Dec. 31, 2018	2,447,660	1,824	2,791,555	(428,307)	14,433	2,379,505	67,477	678	68,155
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net proceeds from sale of common shares	31,020	17	31,003			31,020
Restricted share award grants, net	355	2	640	(287)		355
Purchase of OP Units	105						105		105
Dividends/distributions declared	(43,694)			(42,536)		(42,536)	(1,158)		(1,158)
Preferred distributions	(284)			(284)		(284)
Distributions	(47)							(47)	(47)
Change in market value of Redeemable Noncontrolling Interest	(290)		(290)	0		(290)
Change in fair value of interest rate swap agreements	(3,476)				(3,476)	(3,476)
Net income	11,426			11,057		11,057	305	64	369
Adjustment for Noncontrolling Interests ownership in Operating Partnership	0		(149)			(149)	149		149
Balance at Mar. 31, 2019	$ 2,442,326	$ 1,843	$ 2,822,520	$ (460,357)	$ 10,957	$ 2,374,963	$ 66,668	$ 695	$ 67,363