Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Document Period End Date	Sep. 30, 2015
PROPERTIES:
Operating properties, net of accumulated depreciation of $385,657 and $324,543 in 2015 and 2014, respectively	$ 2,160,655	$ 2,181,684
Projects under development	53,118	91,615
Land	17,829	21,646
Total properties	2,231,602	2,294,945
Real Estate Held-for-sale	50,491	0
Cash and cash equivalents	5,331	0
Restricted cash	4,486	5,042
Notes and accounts receivable, net of allowance for doubtful accounts of $1,736 and $1,643 in 2015 and 2014, respectively	9,513	10,732
Deferred rents receivable	63,738	57,939
Investment in unconsolidated joint ventures	103,470	100,498
Intangible assets, net of accumulated amortization of $96,349 and $76,050 in 2015 and 2014, respectively	131,858	163,244
Other assets	37,118	34,930
Total assets	2,637,607	2,667,330
LIABILITIES AND EQUITY
Notes payable	779,570	792,344
Accounts payable and accrued expenses	66,049	76,240
Deferred income	24,132	23,277
Intangible liabilities, net of accumulated amortization of $24,464 and $16,897 in 2015 and 2014, respectively	62,019	70,020
Other liabilities	30,407	31,991
Disposal Group, Including Discontinued Operation, Liabilities, Current	2,843	0
Total liabilities	965,020	993,872
STOCKHOLDERS' INVESTMENT:
Common stock, $1 par value, 350,000,000 shares authorized, 220,255,502 and 220,082,610 shares issued in 2015 and 2014, respectively	220,256	220,083
Additional paid-in capital	1,721,856	1,720,972
Treasury stock at cost, 5,584,743 and 3,570,082 shares in 2015 and 2014, respectively	(105,531)	(86,840)
Distributions in excess of cumulative net income	(163,994)	(180,757)
Total equity	1,672,587	1,673,458
Total liabilities and equity	$ 2,637,607	$ 2,667,330