Consolidated Statement of Equity - USD ($) $ in Thousands	Total	Parent [Member]	Par Value	Additional Paid in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Total Noncontrolling Interests	Operating Partnership Noncontrolling Interest	Partially Owned Properties Noncontrolling Interest
Balance at beginning of period at Dec. 31, 2020	$ 2,715,002	$ 2,641,297	$ 2,096	$ 3,303,231	$ (658,171)	$ (5,859)	$ 73,705	$ 73,302	$ 403
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net proceeds from sale of common shares	52,432	52,432	28	52,404
Restricted share award grants, net	(993)	(993)	4	(333)	(664)
Purchase of OP Units	(269)						(269)	(269)
Dividends/distributions declared	(50,254)	(49,011)			(49,011)		(1,243)	(1,243)
Preferred distributions	(13)	(13)			(13)
Distributions	(73)						(73)		(73)
Change in market value of Redeemable Noncontrolling Interest in Operating Partnership	873	873		(23)	896
Change in fair value of interest rate swap agreements	797	797				797
Adjustment for Noncontrolling Interests ownership in Operating Partnership	0	1,136		1,136			(1,136)	(1,136)
Net income	17,729	17,194			17,194		535	459	76
Balance at end of period at Mar. 31, 2021	2,735,231	2,663,712	2,128	3,356,415	(689,769)	(5,062)	71,519	71,113	406
Balance at beginning of period at Dec. 31, 2021	2,987,033	2,836,308	2,247	3,610,954	(776,001)	(892)	150,725	150,241	484
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net proceeds from sale of common shares	5,032	5,032	3	5,029
Restricted share award grants, net	(300)	(300)	3	118	(421)
Purchase of OP Units	(184)						(184)	(184)
Dividends/distributions declared	(54,619)	(51,879)			(51,879)		(2,740)	(2,740)
Contributions	569						569		569
Distributions	(55)						(55)		(55)
Change in market value of Redeemable Noncontrolling Interest in Operating Partnership	717	717			717
Change in fair value of interest rate swap agreements	1,379	1,379				1,379
Adjustment for Noncontrolling Interests ownership in Operating Partnership	0	(217)		(217)			217	217
Net income	13,866	13,092			13,092		774	692	82
Balance at end of period at Mar. 31, 2022	$ 2,953,438	$ 2,804,132	$ 2,253	$ 3,615,884	$ (814,492)	$ 487	$ 149,306	$ 148,226	$ 1,080