SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 Percent	Dec. 31, 2010	Dec. 31, 2009	Sep. 30, 2010
Tenant-in-common interest [Abstract]
Ordinary taxable income distribution requirement, minimum (in hundredths)	90.00%
Federal Income Tax Treatment of Share Distributions [Abstract]
Estimated useful lives for buildings (in years)	40
Estimated useful lives of improvements and personal property - minimum (in years)	3
Estimated useful lives of improvements and personal property - maximum (in years)	15
Depreciation expense for continuing and discontinued operations	$ 48,648,000	$ 48,442,000	$ 45,195,000
Capitalization of development costs ceases threshold description	When the property becomes 80% occupied or one year after completion of the shell construction (whichever comes first)
Percentage of property occupation by tenants when development cost ceased being capitalized (in hundredths)	80.00%
Length of time after project completion when development costs are no longer capitalized (in year)	one
Repaid mortgage loan				8,770,000
Amortization of loan costs for continuing operations	1,053,000	1,056,000	1,032,000
Leasing costs amortization expense	6,487,000	6,703,000	6,366,000
Above and below market leases Increase (decrease) rental Income	(341,000)	(478,000)	(11,000)
Amortization expense for in-place lease intangibles	2,316,000	3,205,000	2,443,000
Projected amortization of in-place lease intangibles for the next five years [Abstract]
2012	3,485,000
2013	1,528,000
2014	919,000
2015	719,000
2016	1,028,000
Acquired operating properties [Abstract]
Total cost of properties purchased	88,592,000	23,555,000
Total amount allocated to real estate properties	80,624,000	19,545,000
Total purchase price to land	13,872,000	7,914,000
Acquired Finite-Lived Intangible Assets [Line Items]
Acquisition-related costs expensed	252,000	72,000
Leases, Acquired-in-Place [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangibles acquired associated with purchase of Real Estate	6,949,000	3,118,000
Above Market Lease [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangibles acquired associated with purchase of Real Estate	1,693,000	923,000
Below Market Lease [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Intangibles acquired associated with purchase of Real Estate	$ 674,000	$ 31,000
Lakeview Business Center, Charlotte, North Carolina [Member]
Acquired operating properties [Abstract]
Real estate properties (in square feet)	127,000
Ridge Creek Distribution Center II, Charlotte, North Carolina [Member]
Acquired operating properties [Abstract]
Real estate properties (in square feet)	300,000
Broadway Industrial Park, Tempe, Arizona [Member]
Acquired operating properties [Abstract]
Real estate properties (in square feet)	24,000
Tampa Industrial Portfolio, Tampa, Florida [Member]
Acquired operating properties [Abstract]
Real estate properties (in square feet)	1,147,000
Rittiman Distribution Center, San Antonio, Texas [Member]
Acquired operating properties [Abstract]
Real estate properties (in square feet)	172,000
Commerce Park 2 & 3, Charlotte, North [Member]
Acquired operating properties [Abstract]
Real estate properties (in square feet)		193,000
Ocean View Corporate Center, San Diego, California [Member]
Acquired operating properties [Abstract]
Real estate properties (in square feet)		274,000
East University Distribution Center III, Phoenix, Arizona [Member]
Acquired operating properties [Abstract]
Real estate properties (in square feet)		32,000
Common Stock [Member]
Federal Income Tax Treatment of Share Distributions [Abstract]
Ordinary income distributions (in dollars per share)	$ 1.6852	$ 1.4775	$ 1.7534
Return of capital distributions (in dollars per share)	$ 0.3948	$ 0.6025	$ 0.3266
Total Common Distributions (in dollars per share)	$ 2.0800	$ 2.0800	$ 2.0800
University Business Centers [Member]
Controlling interest Joint ventures [Abstract]
Controlling interest in joint ventures (in hundredths)	80.00%
Joint ventures' assets, liabilities, revenues and expenses with noncontrolling interests (in hundredths)	100.00%
Castilian Research Center [Member]
Controlling interest Joint ventures [Abstract]
Controlling interest in joint ventures (in hundredths)	80.00%
Joint ventures' assets, liabilities, revenues and expenses with noncontrolling interests (in hundredths)	100.00%
Industry Distribution Center II [Member]
Tenant-in-common interest [Abstract]
Equity method of accounting is used for undivided tenant-in-common interest in Industry Distribution Center II (in hundredths)	50.00%