Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Document Period End Date	Jun. 30, 2015
PROPERTIES:
Operating properties, net of accumulated depreciation of $360,700 and $324,543 in 2015 and 2014, respectively	$ 2,203,091	$ 2,181,684
Projects under development	16,207	91,615
Land	12,355	21,646
Total properties	2,231,653	2,294,945
Real estate assets and other assets held for sale, net of accumulated depreciation and amortization of $20,884 in 2015	86,775	0
Cash and cash equivalents	1,972	0
Restricted cash	5,430	5,042
Notes and accounts receivable, net of allowance for doubtful accounts of $2,006 and $1,643 in 2015 and 2014, respectively	13,299	10,732
Deferred rents receivable	63,755	57,939
Investment in unconsolidated joint ventures	103,665	100,498
Intangible assets, net of accumulated amortization of $88,776 and $76,050 in 2015 and 2014, respectively	139,557	163,244
Other assets	39,360	34,930
Total assets	2,685,466	2,667,330
LIABILITIES AND EQUITY
Notes payable	849,772	792,344
Accounts payable and accrued expenses	56,700	76,240
Deferred income	23,290	23,277
Intangible liabilities, net of accumulated amortization of $21,925 and $16,897 in 2015 and 2014, respectively	64,557	70,020
Other liabilities	33,318	31,991
Disposal Group, Including Discontinued Operation, Liabilities, Current	3,132	0
Total liabilities	1,030,769	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	1,721,560	1,720,972
Treasury stock at cost, 3,570,082 shares in 2015 and 2014	(86,840)	(86,840)
Distributions in excess of cumulative net income	(200,279)	(180,757)
Total equity	1,654,697	1,673,458
Total liabilities and equity	$ 2,685,466	$ 2,667,330