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, 2017	$ 2,215,639	$ 84	$ 1,596,514	$ 2,614	$ (32,013)	$ 1,567,199	$ 648,440
Balance (in Shares) at Dec. 31, 2017		83,708,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0		642			642	(642)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		38,000
Repurchase of Common Shares	(31,961)	$ (2)	(31,959)			(31,961)
Repurchase of Common Shares (in shares)		(1,304,000)
Dividends/distribution declared ($0.28 and $0.27 per Common Share/OP Unit for Three Months Ended March 31, 2019 and 2018)	(23,983)				(22,262)	(22,262)	(1,721)
Employee and trustee stock compensation, net	3,811		95			95	3,716
Employee and trustee stock compensation, net (in Shares)		9,000
Noncontrolling interest distributions	(695)						(695)
Comprehensive (loss) income	1,856			4,762	7,419	12,181	(10,325)
Reallocation of noncontrolling interests	0		(1,225)			(1,225)	1,225
Ending Balance at Mar. 31, 2018	2,164,667	$ 82	1,564,067	7,376	(46,856)	1,524,669	639,998
Balance (in Shares) at Mar. 31, 2018		82,451,000
Beginning 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		83,708,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of Common Shares	$ (55,100)
Repurchase of Common Shares (in shares)	(2,294,235)
Ending Balance at Dec. 31, 2018	$ 2,081,947	$ 82	1,548,603	516	(89,696)	1,459,505	622,442
Balance (in Shares) at Dec. 31, 2018	81,557,472	81,557,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	$ 0		2,953			2,953	(2,953)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		175,000
Repurchase of Common Shares (in shares)	0
Issuance of Common Shares	$ 27,834	$ 1	27,833			27,834
Issuance of Common Shares (in Shares)		971,000
Dividends/distribution declared ($0.28 and $0.27 per Common Share/OP Unit for Three Months Ended March 31, 2019 and 2018)	(24,916)				(23,135)	(23,135)	(1,781)
Employee and trustee stock compensation, net	3,454		94			94	3,360
Employee and trustee stock compensation, net (in Shares)		5,000
Noncontrolling interest distributions	(3,237)						(3,237)
Noncontrolling interest contributions	32,191						32,191
Comprehensive (loss) income	(10,921)			(11,537)	12,197	660	(11,581)
Reallocation of noncontrolling interests	0		(1,980)			(1,980)	1,980
Ending Balance at Mar. 31, 2019	$ 2,106,352	$ 83	$ 1,577,503	$ (11,021)	$ (100,634)	$ 1,465,931	$ 640,421
Balance (in Shares) at Mar. 31, 2019	82,708,361	82,708,000