CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY AND COMPREHENSIVE INCOME (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Parent [Member]	Noncontrolling Interest [Member]
Balance at Dec. 31, 2010	$ 587,522	$ 40	$ 303,823	$ (2,857)	$ 17,206	$ 318,212	$ 269,310
Balance (in Shares) at Dec. 31, 2010		40,254,000
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0	0	40	0	0	40	(40)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		10,000
Issuance of OP Units to Acquire Real Estate	0
Dividends declared ($0.18 per Common Share)	(7,505)	0	0	0	(7,258)	(7,258)	(247)
Vesting of employee Restricted Share and LTIP awards	832	0	132	0	0	132	700
Vesting of employee Restricted Share and LTIP awards (in Shares)		95,000
Common Shares issued under Employee Share Purchase Plan	24	0	24	0	0	24	0
Common Shares issued under Employee Share Purchase Plan (in Shares)		1,000
Issuance of LTIP Unit awards to employees	2,441	0	0	0	0	0	2,441
Issuance of Common Shares to trustees	22	0	22	0	0	22	0
Issuance of Common Shares to trustees (in Shares)		0
Exercise of Share options	7	0	7	0	0	7	0
Exercise of Share options (in Shares)		1,000
Employee Restricted Shares cancelled	(724)	0	(724)	0	0	(724)	0
Employee Restricted Shares cancelled (in Shares)		(40,000)
Noncontrolling interest distributions	(83)	0	0	0	0	0	(83)
Balance before adjustment towards comprehensive income	582,536	40	303,324	(2,857)	9,948	310,455	272,081
Balance before adjustment towards comprehensive income (in Shares)		40,321,000
Comprehensive income (loss):
Net income (loss)	9,652	0	0	0	9,423	9,423	229
Unrealized income (loss) on valuation of swap agreements	(307)	0	0	(241)	0	(241)	(66)
Reclassification of realized interest on swap agreements	885	0	0	736	0	736	149
Total comprehensive income (loss)	10,230	0	0	495	9,423	9,918	312
Balance at Mar. 31, 2011	592,766	40	303,324	(2,362)	19,371	320,373	272,393
Balance (in Shares) at Mar. 31, 2011		40,321,000
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	42,586,376	42,586,000
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership	0	0	2,534	0	0	2,534	(2,534)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		161,000
Issuance of Common Shares, net of issuance costs	17,761	1	17,760	0	0	17,761	0
Issuance of Common Shares, net of issuance costs (in Shares)		808,000
Issuance of OP Units to Acquire Real Estate	2,279	0	0	0	0	0	2,279
Dividends declared ($0.18 per Common Share)	(8,095)	0	0	0	(7,808)	(7,808)	(287)
Vesting of employee Restricted Share and LTIP awards	886	0	40	0	0	40	846
Vesting of employee Restricted Share and LTIP awards (in Shares)		22,000
Common Shares issued under Employee Share Purchase Plan	20	0	20	0	0	20	0
Common Shares issued under Employee Share Purchase Plan (in Shares)		1,000
Issuance of LTIP Unit awards to employees	2,577	0	0	0	0	0	2,577
Issuance of Common Shares to trustees	84	0	84	0	0	84	0
Issuance of Common Shares to trustees (in Shares)		0
Exercise of Share options	23	0	23	0	0	23	0
Exercise of Share options (in Shares)		1,000
Employee Restricted Shares cancelled	(150)	0	(150)	0	0	(150)	0
Employee Restricted Shares cancelled (in Shares)		(7,000)
Noncontrolling interest distributions	(3,450)	0	0	0	0	0	(3,450)
Noncontrolling Interest contributions	38,578	0	0	0	0	0	38,578
Balance before adjustment towards comprehensive income	819,822	44	368,978	(3,913)	31,509	396,618	423,204
Balance before adjustment towards comprehensive income (in Shares)		43,572,000
Comprehensive income (loss):
Net income (loss)	2,823	0	0	0	4,010	4,010	(1,187)
Unrealized income (loss) on valuation of swap agreements	57	0	0	124	0	124	(67)
Reclassification of realized interest on swap agreements	637	0	0	470	0	470	167
Total comprehensive income (loss)	3,517	0	0	594	4,010	4,604	(1,087)
Balance at Mar. 31, 2012	$ 823,339	$ 44	$ 368,978	$ (3,319)	$ 35,519	$ 401,222	$ 422,117
Balance (in Shares) at Mar. 31, 2012	43,572,025	43,572,000