CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Shares	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	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	438			438	(438)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		25,000
Dividends declared ($0.27 and $0.26 per Common Share/OP Unit for Three Months Ended March 31, 2018 and 2017)	(23,366)				(21,749)	(21,749)	(1,617)
Employee and trustee stock compensation, net	4,235		94			94	4,141
Employee and trustee stock compensation, net (in Shares)		7,000
Noncontrolling interest distributions	(3,822)						(3,822)
Noncontrolling interest contributions	20,269						20,269
Reallocation of noncontrolling interests	0		(5,693)			(5,693)	5,693
Comprehensive income	21,052			1,236	15,631	16,867	4,185
Ending Balance at Mar. 31, 2017	2,196,493	$ 84	1,589,765	438	(11,753)	1,578,534	617,959
Balance (in Shares) at Mar. 31, 2017		83,630,000
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		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)	(1,304,194)	(1,304,000)
Dividends declared ($0.27 and $0.26 per Common Share/OP Unit for Three Months Ended March 31, 2018 and 2017)	$ (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)
Reallocation of noncontrolling interests	0		(1,225)			(1,225)	1,225
Comprehensive income	1,856			4,762	7,419	12,181	(10,325)
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	82,450,745	82,451,000