Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
ASSETS
Operating (including $278,885 and $278,826 of consolidated variable interest entities, respectively)	$ 4,497,312	$ 4,490,960
Construction-in-progress	327,840	288,714
Real Estate Investment Property, At Cost, Total	4,825,152	4,779,674
Less accumulated depreciation and amortization (including $13,801 and $12,024 of consolidated variable interest entities, respectively)	(1,257,767)	(1,224,295)
Net real estate	3,567,385	3,555,379
Cash and cash equivalents	31,274	36,988
Accounts and notes receivable, net	77,154	73,861
Mortgage notes receivable, net	55,693	55,648
Investment in real estate partnership	33,131	33,169
Prepaid expenses and other assets	131,192	132,659
Debt issuance costs, net of accumulated amortization of $10,881 and $10,140, respectively	10,103	10,861
TOTAL ASSETS	3,905,932	3,898,565
Liabilities
Mortgages payable (including $204,681 and $205,299 of consolidated variable interest entities, respectively)	747,978	760,789
Capital lease obligations	71,687	71,693
Notes payable	299,595	299,575
Senior notes and debentures	1,076,635	1,076,545
Accounts payable and accrued expenses	126,715	120,929
Dividends payable	47,977	47,685
Security deposits payable	13,065	12,957
Other liabilities and deferred credits	94,501	103,379
Total liabilities	2,478,153	2,493,552
Commitments and contingencies (Note 6)
Redeemable noncontrolling interests	94,249	94,420
Shareholders' equity
Preferred shares, authorized 15,000,000 shares, $.01 par: 5.417% Series 1 Cumulative Convertible Preferred Shares, (stated at liquidation preference $25 per share), 399,896 shares issued and outstanding	9,997	9,997
Common shares of beneficial interest, $.01 par, 100,000,000 shares authorized, 65,239,183 and 64,815,446 shares issued and outstanding, respectively	653	648
Additional paid-in capital	1,910,200	1,875,525
Accumulated dividends in excess of net income	(600,024)	(586,970)
Accumulated other comprehensive loss	(10,773)	(12,388)
Total shareholders' equity of the Trust	1,310,053	1,286,812
Noncontrolling interests	23,477	23,781
Total shareholders' equity	1,333,530	1,310,593
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 3,905,932	$ 3,898,565