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) Retained Earnings	Total Common Shareholders’ Equity	Noncontrolling Interests
Beginning Balance at Dec. 31, 2014	$ 1,435,957	$ 68	$ 1,027,861	$ (4,005)	$ 31,617	$ 1,055,541	$ 380,416
Balance (in Shares) at Dec. 31, 2014		68,109,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0		2,451			2,451	(2,451)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		101,000
Issuance of Common Shares, net of issuance costs	64,417	$ 2	64,415			64,417
Issuance of Common Shares, net of issuance costs (in Shares)		1,973,000
Dividends declared ($1.05, $1.16 and $1.22 per Common Share/OP Unit for Year Ended December 31, 2017, 2016 and 2015 respectively)	(90,666)				(84,683)	(84,683)	(5,983)
Acquisition of noncontrolling interests	(7,970)		(4,409)			(4,409)	(3,561)
Employee and trustee stock compensation, net	8,644		1,921			1,921	6,723
Employee and trustee stock compensation, net (in Shares)		75,000
Noncontrolling interest distributions	(74,950)						(74,950)
Noncontrolling interest contributions	35,489						35,489
Comprehensive income	150,433			(458)	65,708	65,250	85,183
Ending Balance at Dec. 31, 2015	1,521,354	$ 70	1,092,239	(4,463)	12,642	1,100,488	420,866
Balance (in Shares) at Dec. 31, 2015		70,258,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0	$ 1	7,891			7,892	(7,892)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		351,000
Issuance of Common Shares, net of issuance costs	450,130	$ 13	450,117			450,130
Issuance of Common Shares, net of issuance costs (in Shares)		12,961,000
Issuance of OP Units to acquire real estate	31,429						31,429
Dividends declared ($1.05, $1.16 and $1.22 per Common Share/OP Unit for Year Ended December 31, 2017, 2016 and 2015 respectively)	(97,806)				(91,053)	(91,053)	(6,753)
Acquisition of noncontrolling interests	(18,379)		7,546			7,546	(25,925)
Employee and trustee stock compensation, net	13,694		926			926	12,768
Employee and trustee stock compensation, net (in Shares)		28,000
Change in control of previously unconsolidated investment	(75,713)						(75,713)
Windfall tax benefit	555		555			555
Noncontrolling interest distributions	(80,769)						(80,769)
Noncontrolling interest contributions	295,108						295,108
Reallocation of noncontrolling interests	0		35,652			35,652	(35,652)
Comprehensive income	138,522			3,665	72,776	76,441	62,081
Ending 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	83,597,741	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		1,541			1,541	(1,541)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		87,000
Dividends declared ($1.05, $1.16 and $1.22 per Common Share/OP Unit for Year Ended December 31, 2017, 2016 and 2015 respectively)	(94,301)				(87,848)	(87,848)	(6,453)
Employee and trustee stock compensation, net	11,155		698			698	10,457
Employee and trustee stock compensation, net (in Shares)		23,000
Noncontrolling interest distributions	(32,805)						(32,805)
Noncontrolling interest contributions	85,206						85,206
Reallocation of noncontrolling interests	0		(651)			(651)	651
Comprehensive income	68,259			3,412	61,470	64,882	3,377
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