CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Parent	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Noncontrolling Interest
Balance at Dec. 31, 2011	$ 769,309	$ 384,114	$ 43	$ 348,667	$ (3,913)	$ 39,317	$ 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 (in Shares)			161,000
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0	2,534	0	2,534	0	0	(2,534)
Issuance of Common Shares, net of issuance costs (in Shares)			808,000
Issuance of Common Shares, net of issuance costs	17,761	17,761	1	17,760	0	0	0
Issuance of OP Units to Acquire Real Estate	2,279	0	0	0	0	0	2,279
Dividends declared ($0.54 per Common Share)	(8,095)	(7,808)	0	0	0	(7,808)	(287)
Vesting of employee Restricted Share and LTIP awards (in Shares)			22,000
Vesting of employee Restricted Share and LTIP awards	886	40	0	40	0	0	846
Common Shares issued under Employee Share Purchase Plan (in Shares)			1,000
Common Shares issued under Employee Share Purchase Plan	20	20	0	20	0	0	0
Issuance Of LTIP Unit Awards To Employees	2,577	0	0	0	0	0	2,577
Issuance of Common Shares to trustees (in Shares)			0
Issuance of Common Shares to trustees	84	84	0	84	0	0	0
Exercise of Share options (in Shares)			1,000
Exercise of Share options	23	23	0	23	0	0	0
Employee Restricted Shares cancelled (in Shares)			(7,000)
Employee Restricted Shares cancelled	(150)	(150)	0	(150)	0	0	0
Noncontrolling interest distributions	(3,450)	0	0	0	0	0	(3,450)
Noncontrolling Interest, Increase from Contributions	38,578	0	0	0	0	0	38,578
Balance before adjustment towards comprehensive income (in Shares)			43,572,000
Balance before adjustment towards comprehensive income	819,822	396,618	44	368,978	(3,913)	31,509	423,204
Comprehensive (loss) income:
Net income	2,823	4,010	0	0	0	4,010	(1,187)
Unrealized (loss) income on valuation of swap agreements	57	124	0	0	124	0	(67)
Reclassification of realized interest on swap agreements	637	470	0	0	470	0	167
Total comprehensive (loss) income	3,517	4,604	0	0	594	4,010	(1,087)
Balance at Mar. 31, 2012	823,339	401,222	44	368,978	(3,319)	35,519	422,117
Balance (in Shares) at Mar. 31, 2012			43,572,000
Balance at Dec. 31, 2012	1,070,256	622,797	52	581,925	(4,307)	45,127	447,459
Balance (in Shares) at Dec. 31, 2012	52,482,598		52,482,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)			20,000
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0	438	0	438	0	0	(438)
Issuance of Common Shares, net of issuance costs (in Shares)			1,997,000
Issuance of Common Shares, net of issuance costs	52,818	52,818	2	52,816	0	0	0
Issuance of OP Units to Acquire Real Estate	0
Dividends declared ($0.54 per Common Share)	(11,757)	(11,409)	0	0	0	(11,409)	(348)
Vesting of employee Restricted Share and LTIP awards (in Shares)			9,000
Vesting of employee Restricted Share and LTIP awards	1,305	53	0	53	0	0	1,252
Common Shares issued under Employee Share Purchase Plan (in Shares)			1,000
Common Shares issued under Employee Share Purchase Plan	19	19	0	19	0	0	0
Issuance of Common Shares to trustees (in Shares)			0
Issuance of Common Shares to trustees	103	103	0	103	0	0	0
Exercise of Share options (in Shares)			8,000
Exercise of Share options	143	143	0	143	0	0	0
Employee Restricted Shares cancelled (in Shares)			(3,000)
Employee Restricted Shares cancelled	(83)	(83)	0	(83)	0	0	0
Acquisition Of Interest In Unconsolidated Affiliate Investment In Unconsolidated Affiliates	(33,949)	0	0	0	0	0	(33,949)
Noncontrolling interest distributions	(2,842)	0	0	0	0	0	(2,842)
Balance before adjustment towards comprehensive income (in Shares)			54,514,000
Balance before adjustment towards comprehensive income	1,076,013	664,879	54	635,414	(4,307)	33,718	411,134
Comprehensive (loss) income:
Net income	11,179	9,623	0	0	0	9,623	1,556
Unrealized (loss) income on valuation of swap agreements	(1,092)	(974)	0	0	(974)	0	(118)
Reclassification of realized interest on swap agreements	592	349	0	0	349	0	243
Total comprehensive (loss) income	10,679	8,998	0	0	(625)	9,623	1,681
Balance at Mar. 31, 2013	$ 1,086,692	$ 673,877	$ 54	$ 635,414	$ (4,932)	$ 43,341	$ 412,815
Balance (in Shares) at Mar. 31, 2013	54,514,365		54,514,000