Consolidated Statements Of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
REVENUE
Rental income	$ 538,701	$ 522,651	$ 510,777
Other property income	9,260	14,545	12,849
Mortgage interest income	5,098	4,601	4,943
Total revenue	553,059	541,797	528,569
EXPENSES
Rental expenses	109,549	110,519	108,344
Real estate taxes	60,620	58,663	57,866
General and administrative	28,985	24,189	22,032
Litigation provision	0	330	16,355
Depreciation and amortization	126,208	118,878	114,443
Total operating expenses	325,362	312,579	319,040
OPERATING INCOME	227,697	229,218	209,529
Other interest income	218	256	1,894
Interest expense	(98,465)	(101,882)	(108,781)
Early extinguishment of debt	296	(2,801)	(2,639)
Income from real estate partnerships	1,808	1,060	1,322
INCOME FROM CONTINUING OPERATIONS	131,554	125,851	101,325
DISCONTINUED OPERATIONS
Discontinued operations - income	957	976	1,249
Discontinued operations - gain on deconsolidation of VIE	2,026	0	0
Discontinued operation - gain on sale of real estate	15,075	1,000	1,298
Results from discontinued operations	18,058	1,976	2,547
INCOME BEFORE GAIN ON SALE OF REAL ESTATE	149,612	127,827	103,872
Gain on sale of real estate	0	410	0
NET INCOME	149,612	128,237	103,872
Net income attributable to noncontrolling interests	(5,695)	(5,447)	(5,568)
NET INCOME ATTRIBUTABLE TO THE TRUST	143,917	122,790	98,304
Dividends on preferred shares	(541)	(541)	(541)
NET INCOME AVAILABLE FOR COMMON SHAREHOLDERS	$ 143,376	$ 122,249	$ 97,763
EARNINGS PER COMMON SHARE, BASIC
Continuing operations	$ 2.00	$ 1.95	$ 1.59
Discontinued operations	$ 0.29	$ 0.03	$ 0.04
Gain on sale of real estate		$ 0.01
Earnings Per Share, Basic, Total	$ 2.29	$ 1.99	$ 1.63
Weighted average common shares outstanding-basic	62,438	61,182	59,704
EARNINGS PER COMMON SHARE, DILUTED
Continuing operations	$ 1.99	$ 1.94	$ 1.59
Discontinued operations	$ 0.29	$ 0.03	$ 0.04
Gain on sale of real estate		$ 0.01
Earnings Per Share, Diluted, Total	$ 2.28	$ 1.98	$ 1.63
Weighted average number of common shares-diluted	62,603	61,324	59,830