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
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	5,679			5,680	(5,680)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		249,000
Issuance of Common Shares, net of issuance costs	35,220	$ 1	35,219			35,220
Issuance of Common Shares, net of issuance costs (in Shares)		1,050,000
Issuance of OP Units to acquire real estate	29,336						29,336
Dividends declared	(19,345)				(17,872)	(17,872)	(1,473)
Acquisition of noncontrolling interests	(18,379)		7,569			7,569	(25,948)
Employee and trustee stock compensation, net	4,019		208			208	3,811
Employee and trustee stock compensation, net (in Shares)		9,000
Noncontrolling interest distributions	(36,174)						(36,174)
Noncontrolling interest contributions	46,343						46,343
Comprehensive income	66,102			(7,004)	28,925	21,921	44,181
Balance at Mar. 31, 2016	1,628,476	$ 72	1,140,914	(11,467)	23,695	1,153,214	475,262
Balance (in Shares) at Mar. 31, 2016		71,566,000
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
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		438			438	(438)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		25,000
Dividends declared	(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
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	83,630,051	83,630,000