CONSOLIDATED STATEMENTS OF SHAREHOLDERS’ EQUITY AND COMPREHENSIVE INCOME (USD $) In Thousands	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, 2009	$ 532,477	$ 40	$ 299,014	$ (2,994)	$ 16,125	$ 312,185	$ 220,292
Balance (in Shares) at Dec. 31, 2009		39,787
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership			2,174			2,174	(2,174)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		257
Dividends declared ($0.36 per Common Share)	(14,847)				(14,466)	(14,466)	(381)
Vesting of employee Restricted Share and LTIP awards	1,950		1,062			1,062	888
Vesting of employee Restricted Share and LTIP awards (in Shares)		133
Common Shares issued under Employee Share Purchase Plan	50		50			50
Common Shares issued under Employee Share Purchase Plan (in Shares)		3
Issuance of Common Shares to trustees	190		190			190
Issuance of Common Shares to trustees (in Shares)		13
Exercise of trustees options	101		101			101
Exercise of trustees options (in Shares)		7
Employee Restricted Shares cancelled	(966)		(966)			(966)
Employee Restricted Shares cancelled (in Shares)		(57)
Noncontrolling interest distributions	(523)						(523)
Noncontrolling interest contributions	19,476						19,476
Balance before adjustment towards comprehensive income	537,908	40	301,625	(2,994)	1,659	300,330	237,578
Balance before adjustment towards comprehensive income (in Shares)		40,143
Net income (loss)	39,004				17,928	17,928	21,076
Unrealized loss on valuation of swap agreements	(1,727)			(1,701)		(1,701)	(26)
Reclassification of realized interest on swap agreements	1,501			1,324		1,324	177
Total comprehensive income (loss)	38,778			(377)	17,928	17,551	21,227
Balance at Jun. 30, 2010	576,686	40	301,625	(3,371)	19,587	317,881	258,805
Balance (in Shares) at Jun. 30, 2010		40,143
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
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership			49			49	(49)
Conversion of OP Units to Common Shares by limited partners of the Operating Partnership (in Shares)		11
Dividends declared ($0.36 per Common Share)	(15,009)				(14,517)	(14,517)	(492)
Vesting of employee Restricted Share and LTIP awards	2,223		257			257	1,966
Vesting of employee Restricted Share and LTIP awards (in Shares)		95
Common Shares issued under Employee Share Purchase Plan	45		45			45
Common Shares issued under Employee Share Purchase Plan (in Shares)		2
Issuance of LTIP Unit awards to employees	2,441						2,441
Issuance of Common Shares to trustees	79		79			79
Issuance of Common Shares to trustees (in Shares)		8
Exercise of trustees options	7		7			7
Exercise of trustees options (in Shares)		1
Employee Restricted Shares cancelled	(724)		(724)			(724)
Employee Restricted Shares cancelled (in Shares)		(40)
Noncontrolling interest distributions	(705)						(705)
Noncontrolling interest contributions	43,646						43,646
Balance before adjustment towards comprehensive income	619,525	40	303,536	(2,857)	2,689	303,408	316,117
Balance before adjustment towards comprehensive income (in Shares)		40,331
Net income (loss)	34,693				39,657	39,657	(4,964)
Unrealized loss on valuation of swap agreements	(1,557)			(803)		(803)	(754)
Reclassification of realized interest on swap agreements	1,637			1,310		1,310	327
Total comprehensive income (loss)	34,773			507	39,657	40,164	(5,391)
Balance at Jun. 30, 2011	$ 654,298	$ 40	$ 303,536	$ (2,350)	$ 42,346	$ 343,572	$ 310,726
Balance (in Shares) at Jun. 30, 2011		40,331