CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Statement of Cash Flows [Abstract]
Net (loss) income	$ (129,567)	$ (14,262)	$ 37,213
Depreciation	132,347	135,095	133,162
Amortization	12,907	9,505	12,903
Straight Line Rent	1,874	1,467	1,425
Provision for Doubtful Accounts	2,510	1,566	1,656
Amortization Of Deferred Compensation Related To Cash Flows	6,284	8,455	8,071
Loss on Hedge Ineffectiveness	512	1,761	3,409
Discontinued Operation Gain Loss On Disposal Of Discontinued Operation And Gain Loss On Sales Of Real Estate Net Of Tax	12,621	14,473	78,512
Equity In Net Income Loss Of Partnerships	2,312	1,675	2,713
Amortization Of Historic Tax Credits Related To Cash Flows	1,589	2,508	2,494
Impairment Of Assets And Project Costs	140,790	20,187	30,775
Increase (Decrease) in Other Operating Assets	(5,337)	(3,921)	7,779
Increase (Decrease) in Operating Liabilities	(17,063)	(1,030)	1,953
Net Cash Provided by (Used in) Operating Activities	135,661	145,075	136,219
Proceeds from Sale of Real Estate Held-for-investment	52,956	190,442	181,644
Payments to Acquire Commercial Real Estate	319,986	20,000	60,879
Payments for Construction in Process	30,684	41,512	36,456
Payments for Capital Improvements	52,790	71,346	44,785
Leasehold Improvements Cash Flow	486	1,656	2,062
Payments to Acquire Interest in Subsidiaries and Affiliates	25,046	19,184	250
Increase (Decrease) in Lease Acquisition Costs	6,255	5,446	5,261
Increase (Decrease) in Restricted Cash	1,996	2,369	2,682
Proceeds from Distributions Received from Real Estate Partnerships	5,188	2,721	1,472
Net Cash Provided by (Used in) Investing Activities	(379,099)	31,650	30,741
Repayments of Long-term Debt	120,000	(130,000)	182,000
Repayment Of Secured Line Of Credit	(215,000)	130,000	(130,000)
Proceeds from Issuance of Secured Debt	272,044	0	154,692
Repayments of Secured Debt	272,650	76,784	403,691
Debt Instrument, Periodic Payment, Principal	20,761	17,919	16,973
Payments of Financing Costs	3,754	1,918	4,035
Net proceeds from issuance of common shares in public offering	0	0	220,511
Shares Of Beneficial Interest Issued	1,393	3,270	2,983
Payments of Ordinary Dividends, Common Stock	58,085	54,988	48,315
Payments of Ordinary Dividends, Preferred Stock and Preference Stock	15,848	15,848	15,849
Payments to Noncontrolling Interests	5,703	1,703	1,626
Payments for Repurchase of Other Equity	5,776	4,632	2,417
Net Cash Provided by (Used in) Financing Activities	225,860	(170,522)	(166,720)
Cash and Cash Equivalents, Period Increase (Decrease)	(17,578)	6,203	240
Cash and cash equivalents	$ 22,855	$ 40,433	$ 34,230