Consolidated Statements 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
Shareholders' equity, beginning balance at Dec. 31, 2015	$ 1,076,461	$ 870	$ 1,129,286	$ (109,024)		$ 1,021,132	$ 45,451	$ 9,878	$ 55,329
Increase (Decrease) in Stockholders' Equity
Net proceeds from sale of common shares	766,841	473	766,368			766,841
Restricted share award grants, net	4,434	1	4,893	(460)		4,434
Purchase of OP Units	(3,671)						(3,671)		(3,671)
Conversion of OP Units	0	6	11,613			11,619	(11,619)		(11,619)
Dividends/distributions declared	(119,007)		0	(115,901)		(115,901)	(3,106)		(3,106)
Preferred distributions	(1,857)			(1,857)		(1,857)	0		0
Issuance of common shares and OP Units in connection with acquisitions	23,848	10	17,069	0		17,079	6,869	(100)	6,769
Contributions	50						0	50	50
Distributions	(543)							(543)	(543)
Change in market value of Redeemable Noncontrolling Interest in Operating Partnership	(245)		(245)			(245)		0	0
Reclassification of Noncontrolling Interest - partially owned properties	(8,514)							(8,514)	(8,514)
Buyout of Noncontrolling Interests - partially owned properties	(611)		53			53	0	(664)	(664)
Change in fair value of interest rate swap agreements and redeemable equity - property	13,708		0		$ 13,708	13,708
Net (loss) income	31,424			29,981		29,981	825	618	1,443
Adjustment for Noncontrolling Interests ownership in Operating Partnership	0		(8,393)			(8,393)	8,393		8,393
Shareholders' equity, ending 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
Increase (Decrease) in Stockholders' Equity
Net proceeds from sale of common shares	844,669	451	844,218			844,669
Restricted share award grants, net	3,821	2	4,103	(284)		3,821
Purchase of OP Units	(3,886)						(3,886)		(3,886)
Conversion of OP Units		1	929			930	(930)		(930)
Dividends/distributions declared	(158,837)			(153,970)		(153,970)	(4,867)		(4,867)
Preferred distributions	(731)			(731)		(731)
Issuance of common shares and OP Units in connection with acquisitions	44,259	0	0			0	44,259	0	44,259
Contributions	47							47	47
Distributions	(321)							(321)	(321)
Buyout of Noncontrolling Interests - partially owned properties	(2,105)		(2,800)			(2,800)	719	(24)	695
Change in fair value of interest rate swap agreements and redeemable equity - property	(1,073)			(1,317)	244	(1,073)
Net (loss) income	39,473			38,146		38,146	1,136	191	1,327
Adjustment for Noncontrolling Interests ownership in Operating Partnership	0		5,729			5,729	(5,729)		(5,729)
Shareholders' equity, ending 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
Net proceeds from sale of common shares	10,759	6	10,753			10,759
Restricted share award grants, net	6,513	2	6,837	(326)		6,513
Purchase of OP Units	(2,203)						(2,203)		(2,203)
Conversion of OP Units		2	2,523			2,525	(2,525)		(2,525)
Dividends/distributions declared	(172,559)			(167,817)		(167,817)	(4,742)		(4,742)
Preferred distributions	(1,340)			(1,340)		(1,340)
Distributions	(173)							(173)	(173)
Change in market value of Redeemable Noncontrolling Interest in Operating Partnership	509		146	363		509		0	0
Change in fair value of interest rate swap agreements and redeemable equity - property	481				481	481
Net (loss) income	58,039			56,230		56,230	1,576	233	1,809
Adjustment for Noncontrolling Interests ownership in Operating Partnership	0		(1,527)			(1,527)	1,527		1,527
Shareholders' equity, ending 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