CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Distributions in Excess of Accumulated Earnings	Total Common Shareholders’ Equity	Noncontrolling Interests
Beginning Balance at Dec. 31, 2016	$ 2,178,125	$ 84	$ 1,594,926	$ (798)	$ (5,635)	$ 1,588,577	$ 589,548
Balance (in Shares) at Dec. 31, 2016		83,598,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0	$ 0	730			730	(730)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		41,000
Dividends declared ($0.54 and $0.52 per Common Share/OP Unit for Six Months Ended June 30, 2018 and 2017)	(46,702)				(43,495)	(43,495)	(3,207)
Employee and trustee stock compensation, net	7,002		340			340	6,662
Employee and trustee stock compensation, net (in Shares)		20,000
Noncontrolling interest distributions	(4,507)						(4,507)
Noncontrolling interest contributions	20,505						20,505
Comprehensive income	25,974			278	27,691	27,969	(1,995)
Reallocation of noncontrolling interests	0		(3,927)			(3,927)	3,927
Ending Balance at Jun. 30, 2017	2,180,397	$ 84	1,592,069	(520)	(21,439)	1,570,194	610,203
Balance (in Shares) at Jun. 30, 2017		83,659,000
Beginning Balance at Dec. 31, 2016	$ 2,178,125	$ 84	1,594,926	(798)	(5,635)	1,588,577	589,548
Balance (in Shares) at Dec. 31, 2016		83,598,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of Common Shares (in shares)	0
Ending Balance at Dec. 31, 2017	$ 2,215,639	$ 84	1,596,514	2,614	(32,013)	1,567,199	648,440
Balance (in Shares) at Dec. 31, 2017	83,708,140	83,708,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	$ 0		1,123			1,123	(1,123)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		64,000
Repurchase of Common Shares	$ (55,057)	$ (2)	(55,055)			(55,057)
Repurchase of Common Shares (in shares)	(2,294,235)	(2,294,000)
Dividends declared ($0.54 and $0.52 per Common Share/OP Unit for Six Months Ended June 30, 2018 and 2017)	$ (47,701)				(44,267)	(44,267)	(3,434)
Employee and trustee stock compensation, net	6,113		271			271	5,842
Employee and trustee stock compensation, net (in Shares)		25,000
Noncontrolling interest distributions	(15,640)						(15,640)
Noncontrolling interest contributions	6,550						6,550
Comprehensive income	2,645			7,524	15,084	22,608	(19,963)
Reallocation of noncontrolling interests	0		798			798	(798)
Ending Balance at Jun. 30, 2018	$ 2,112,549	$ 82	$ 1,543,651	$ 10,138	$ (61,196)	$ 1,492,675	$ 619,874
Balance (in Shares) at Jun. 30, 2018	81,502,812	81,503,000