Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Document Period End Date	Jun. 30, 2016
PROPERTIES:
Operating properties, net of accumulated depreciation of $377,418 and $352,350 in 2016 and 2015, respectively	$ 2,186,770	$ 2,194,781
Projects under development	62,567	27,890
Land	17,768	17,829
Total properties	2,267,105	2,240,500
Real Estate Held-for-sale	0	7,246
Cash and cash equivalents	946	2,003
Restricted cash	5,180	4,304
Notes and accounts receivable, net of allowance for doubtful accounts of $1,100 and $1,353 in 2016 and 2015, respectively	13,656	10,828
Deferred rents receivable	74,224	67,258
Investment in unconsolidated joint ventures	114,455	102,577
Intangible assets, net of accumulated amortization of $109,328 and $103,458 in 2016 and 2015, respectively	111,266	124,615
Other assets	36,163	35,989
Total assets	2,622,995	2,595,320
LIABILITIES AND EQUITY
Notes payable	777,485	718,810
Accounts payable and accrued expenses	56,971	71,739
Deferred income	34,158	29,788
Intangible liabilities, net of accumulated amortization of $29,199 and $26,890 in 2016 and 2015, respectively	55,009	59,592
Other liabilities	30,242	30,629
Disposal Group, Including Discontinued Operation, Liabilities, Current	0	1,347
Total liabilities	953,865	911,905
STOCKHOLDERS' INVESTMENT:
Common stock, $1 par value, 350,000,000 shares authorized, 220,436,378 and 220,255,676 shares issued in 2016 and 2015, respectively	220,501	220,256
Additional paid-in capital	1,723,131	1,722,224
Treasury stock at cost, 10,329,082 and 8,742,181 shares in 2016 and 2015, respectively	(148,373)	(134,630)
Distributions in excess of cumulative net income	(127,602)	(124,435)
Nonredeemable Noncontrolling Interest	1,473	0
Total equity	1,669,130	1,683,415
Total liabilities and equity	$ 2,622,995	$ 2,595,320