CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Shares	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Retained Earnings	Total Common Shareholders’ Equity	Noncontrolling Interests
Balance at Dec. 31, 2011	$ 769,309	$ 43	$ 348,667	$ (3,913)	$ 39,317	$ 384,114	$ 385,195
Balance (in Shares) at Dec. 31, 2011		42,586,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0		5,880			5,880	(5,880)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		334,000
Issuance of Common Shares, net of issuance costs	226,721	9	226,712			226,721
Issuance of Common Shares, net of issuance costs (in Shares)		9,510,000
Dividends declared	(34,994)				(33,896)	(33,896)	(1,098)
Issuance of OP Units to acquire real estate	2,279						2,279
Employee and trustee stock compensation, net	6,691		666			666	6,025
Employee and trustee stock compensation, net (in Shares)		52,000
Noncontrolling interest distributions	(160,663)						(160,663)
Noncontrolling interest contributions	172,228						172,228
Balance before adjustment toward comprehensive income	981,571	52	581,925	(3,913)	5,421	583,485	398,086
Balance before adjustment toward comprehensive income (in Shares)		52,482,000
Comprehensive income (loss):
Net income	89,936				39,706	39,706	50,230
Unrealized income (loss) on valuation of swap agreements	(3,519)			(1,815)	0	(1,815)	(1,704)
Reclassification of realized interest on swap agreements	2,268			1,421	0	1,421	847
Total comprehensive (loss) income	88,685			(394)	39,706	39,312	49,373
Balance at Dec. 31, 2012	1,070,256	52	581,925	(4,307)	45,127	622,797	447,459
Balance (in Shares) at Dec. 31, 2012		52,482,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0		1,548			1,548	(1,548)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		93,000
Issuance of Common Shares, net of issuance costs	80,690	4	80,686			80,690
Issuance of Common Shares, net of issuance costs (in Shares)		3,013,000
Dividends declared	(49,159)				(47,495)	(47,495)	(1,664)
Issuance of OP Units to acquire real estate	33,300				0	0	33,300
Employee and trustee stock compensation, net	7,672		1,142			1,142	6,530
Employee and trustee stock compensation, net (in Shares)		55,000
Consolidation of previously unconsolidated investments	(33,949)						(33,949)
Noncontrolling interest distributions	(87,688)						(87,688)
Noncontrolling interest contributions	49,324						49,324
Balance before adjustment toward comprehensive income	1,070,446	56	665,301	(4,307)	(2,368)	658,682	411,764
Balance before adjustment toward comprehensive income (in Shares)		55,643,000
Comprehensive income (loss):
Net income	44,640				40,115	40,115	4,525
Unrealized income (loss) on valuation of swap agreements	3,610			3,541		3,541	69
Reclassification of realized interest on swap agreements	2,892			1,898		1,898	994
Total comprehensive (loss) income	51,142			5,439	40,115	45,554	5,588
Balance at Dec. 31, 2013	1,121,588	56	665,301	1,132	37,747	704,236	417,352
Balance (in Shares) at Dec. 31, 2013	55,643,068	55,643,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0		3,181			3,181	(3,181)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		136,000
Issuance of Common Shares, net of issuance costs	357,459	12	357,447			357,459
Issuance of Common Shares, net of issuance costs (in Shares)		12,237,000
Dividends declared	(82,279)				(77,194)	(77,194)	(5,085)
Issuance of OP Units to acquire real estate	44,051						44,051
Employee and trustee stock compensation, net	8,460		1,932			1,932	6,528
Employee and trustee stock compensation, net (in Shares)		93,000
Noncontrolling interest distributions	(218,152)						(218,152)
Noncontrolling interest contributions	57,969						57,969
Balance before adjustment toward comprehensive income	1,289,096	68	1,027,861	1,132	(39,447)	989,614	299,482
Balance before adjustment toward comprehensive income (in Shares)		68,109,000
Comprehensive income (loss):
Net income	152,146				71,064	71,064	81,082
Unrealized income (loss) on valuation of swap agreements	(9,061)			(7,814)		(7,814)	(1,247)
Reclassification of realized interest on swap agreements	3,776			2,677		2,677	1,099
Total comprehensive (loss) income	146,861			(5,137)	71,064	65,927	80,934
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	68,109,287	68,109,000