CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (Unaudited) - 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, 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	7,382			7,383	(7,383)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		319,000
Issuance of Common Shares, net of issuance costs	141,349	$ 4	141,345			141,349
Issuance of Common Shares, net of issuance costs (in Shares)		4,170,000
Issuance of OP Units to acquire real estate	29,336						29,336
Dividends declared ($0.52 and $0.50 per Common Share/OP Unit for Six Months Ended June 30, 2017 and 2016)	(39,498)				(36,566)	(36,566)	(2,932)
Acquisition of noncontrolling interests	(18,379)		7,569			7,569	(25,948)
Employee and trustee stock compensation, net	6,076		474			474	5,602
Employee and trustee stock compensation, net (in Shares)		26,000
Change in control of previously unconsolidated investment	(75,713)						(75,713)
Noncontrolling interest distributions	(49,135)						(49,135)
Noncontrolling interest contributions	157,409						157,409
Reallocation of noncontrolling interests	0		38,845			38,845	(38,845)
Comprehensive income (loss)	88,118			(10,757)	46,843	36,086	52,032
Ending Balance at Jun. 30, 2016	1,760,917	$ 75	1,287,854	(15,220)	22,919	1,295,628	465,289
Balance (in Shares) at Jun. 30, 2016		74,773,000
Beginning 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
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		730			730	(730)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		41,000
Issuance of Common Shares, net of issuance costs	0	$ 0	0			0
Issuance of Common Shares, net of issuance costs (in Shares)		0
Dividends declared ($0.52 and $0.50 per Common Share/OP Unit for Six Months Ended June 30, 2017 and 2016)	(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
Reallocation of noncontrolling interests	0		(3,927)			(3,927)	3,927
Comprehensive income (loss)	25,974			278	27,691	27,969	(1,995)
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	83,659,353	83,659,000