Consolidated and Combined 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	Operating Partnership	Operating Partnership Partially Owned Properties Noncontrolling Interest	Operating Partnership General Partner	Operating Partnership Limited Partner	Operating Partnership Total Partners’ Capital
Shareholders' equity, beginning balance at Dec. 31, 2014	$ 569,209	$ 508	$ 586,019	$ (51,797)		$ 534,730	$ 33,727	$ 752	$ 34,479
Increase (Decrease) in Stockholders' Equity
Net proceeds from sale of common shares	545,117	361	544,756			545,117
Restricted share award grants, net	2,908	1	3,191	(284)		2,908
Purchase of OP Units	(1,088)						(1,088)		(1,088)
Conversion of OP Units		0	171			171	(171)		(171)
Dividends/distributions declared	(70,886)			(67,542)		(67,542)	(3,344)		(3,344)
Preferred distributions	(1,189)			(1,189)		(1,189)
Issuance of OP Units in connection with acquisitions	10,973						10,973		10,973
Contributions	8,962							8,962	8,962	$ 8,962	$ 8,962
Distributions	(213)		0			0	0	(213)	(213)	(213)	(213)
Change in market value of Redeemable Noncontrolling Interest in Operating Partnership	(73)		(73)			(73)		0	0
Net (loss) income	12,741			11,788		11,788	576	377	953	12,741	377	$ 11,788	$ 576	$ 12,364
Adjustments for Limited Partners ownership in Operating Partnership										0	0	(4,778)	4,778
Adjustment for Noncontrolling Interests ownership in Operating Partnership	0		(4,778)	0		(4,778)	4,778	0	4,778
Shareholders' equity, ending 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 Trust common shares and issuance of common units										545,117		545,117		545,117
Change in market value of Redeemable Limited Partners										(73)		(73)	0	(73)
Trust Restricted share award grants, net										2,908		2,908		2,908
Purchase of OP Units										(1,088)		0	(1,088)	(1,088)
Conversion of OP Units										0		171	(171)
OP Units - distributions										(70,886)		(67,542)	(3,344)	(70,886)
Partners' Capital Account, Preferred Distributions										1,189		1,189	0	1,189
Issuance of OP Units in connection with acquisition										10,973		0	10,973	10,973
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 OP Units in connection with acquisitions	23,848	10	17,069	0		17,079	6,869	(100)	6,769
Contributions	50						0	50	50	50	50
Distributions	(543)							(543)	(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	8,514	8,514
Buyout of Noncontrolling Interests - partially owned properties	(611)		53			53	0	(664)	(664)	(611)	(664)	53	0	53
Change in fair value of interest rate swap agreements and redeemable equity - property	13,708		0		$ 13,708	13,708				13,708				13,708
Net (loss) income	31,424			29,981		29,981	825	618	1,443	31,424	618	29,981	825	30,806
Adjustments for Limited Partners ownership in Operating Partnership										0		(8,393)	8,393
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 Trust common shares and issuance of common units										766,841		766,841		766,841
Change in market value of Redeemable Limited Partners										(245)		(245)		(245)
Trust Restricted share award grants, net										4,434		4,434		4,434
Purchase of OP Units										(3,671)			(3,671)	(3,671)
Conversion of OP Units										0		11,619	(11,619)
OP Units - distributions										(119,007)		(115,901)	(3,106)	(119,007)
Partners' Capital Account, Preferred Distributions										1,857		1,857		1,857
Issuance of OP Units in connection with acquisition										23,848	(100)	17,079	6,869	23,948
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 OP Units in connection with acquisitions	44,259	0	0			0	44,259	0	44,259
Contributions	47							47	47	47	47
Distributions	(321)							(321)	(321)	(321)	(321)
Buyout of Noncontrolling Interests - partially owned properties	(2,105)		(2,800)			(2,800)	719	(24)	695	(2,105)	(24)	(2,800)	719	(2,081)
Change in fair value of interest rate swap agreements and redeemable equity - property	(1,073)			(1,317)	244	(1,073)				(1,073)		(1,317)		(1,073)
Net (loss) income	39,473			38,146		38,146	1,136	191	1,327	39,473	191	38,146	1,136	39,282
Adjustments for Limited Partners ownership in Operating Partnership										0		5,729	(5,729)
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 Trust common shares and issuance of common units										844,669		844,669		844,669
Trust Restricted share award grants, net										3,821		3,821		3,821
Purchase of OP Units										(3,886)			(3,886)	(3,886)
Conversion of OP Units										0		930	(930)
OP Units - distributions										(158,837)		(153,970)	(4,867)	(158,837)
Partners' Capital Account, Preferred Distributions										731		731		731
Issuance of OP Units in connection with acquisition										$ 44,259	$ 0	$ 0	$ 44,259	$ 44,259