REAL ESTATE PROPERTIES (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Real estate properties component balance [Abstract]
Land	$ 235,394,000	$ 221,523,000
Buildings and building improvements	1,056,783,000	985,798,000
Tenant and other improvements	258,267,000	240,134,000
Development	112,149,000	73,722,000
Real estate and development properties	1,662,593,000	1,521,177,000
Less accumulated depreciation	(451,805,000)	(403,187,000)
Real estate, net	1,210,788,000	1,117,990,000
The interest costs capitalized on real estate properties	3,771,000	3,613,000	5,856,000
DEVELOPMENT [Abstract]
Development costs incurred, for the period	42,148,000	9,145,000	35,057,000
Development cost incurred, cumulative	112,149,000	73,722,000
Improvements on developments transferred to real estate properties	2,238,000
Real Estate Property Sales [Abstract]
Recognized Gain	36,000	37,000	60,000
Future Minimum payments receivable [Abstract]
2012	135,253,000
2013	105,237,000
2014	78,751,000
2015	54,516,000
2016	33,948,000
Thereafter	51,043,000
Total minimum receipts	458,748,000
Expenditures for ground leases [Line Items]
Leases terms minimum (in years)	40
Leases terms maximum (in years)	50
Renewal period option minimum (in years)	15
Renewal period option maximum (in years)	35
Total ground lease expenditures for continuing and discontinued operations	705,000	700,000	732,000
Future Total Minimum Ground Lease Payments [Abstract]
2012	707,000
2013	707,000
2014	707,000
2015	707,000
2016	707,000
Thereafter	13,315,000
Total minimum payments	16,850,000
Payment increase interval minimum (in years)	3
Payment increase interval maximum (in years)	10
FLORIDA [Member]
Expenditures for ground leases [Line Items]
Number of properties subject to ground leases	2.00
TEXAS [Member]
Expenditures for ground leases [Line Items]
Number of properties subject to ground leases	2.00
ARIZONA [Member]
Expenditures for ground leases [Line Items]
Number of properties subject to ground leases	1.00
Location Previously Sold [Member]
Real Estate Property Sales [Abstract]
Deferred gain recognized in current period from previous period sales	36,000	37,000	31,000
Butterfield Trail El Paso, TX [Member]
Real Estate Property Sales [Abstract]
Size of property sold (in square feet)			62,000.00
Date of property sale			11/20/09
Net Sales Price			908,000
Basis			(879,000)
Recognized Gain			29,000
Under construction [Member]
Real estate properties component balance [Abstract]
Development	21,652,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	439,000
Development Costs Transferred	8,660,000
Development costs incurred, for the period	12,992,000
Development cost incurred, cumulative	21,652,000
Estimated Total Cumulative Development Costs	34,400,000
Under construction [Member] | World Houston 32, Houston, TX [Member]
Real estate properties component balance [Abstract]
Development	6,210,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	96,000
Development Costs Transferred	1,834,000
Development costs incurred, for the period	4,376,000
Development cost incurred, cumulative	6,210,000
Estimated Total Cumulative Development Costs	6,800,000
Under construction [Member] | Southridge IX, Orlando, FL [Member]
Real estate properties component balance [Abstract]
Development	5,362,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	76,000
Development Costs Transferred	1,987,000
Development costs incurred, for the period	3,375,000
Development cost incurred, cumulative	5,362,000
Estimated Total Cumulative Development Costs	7,100,000
Under construction [Member] | Thousand Oaks 1, San Antonio, TX [Member]
Real estate properties component balance [Abstract]
Development	2,409,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	36,000
Development Costs Transferred	865,000
Development costs incurred, for the period	1,544,000
Development cost incurred, cumulative	2,409,000
Estimated Total Cumulative Development Costs	4,600,000
Under construction [Member] | Thousand Oaks 2, San Antonio, TX [Member]
Real estate properties component balance [Abstract]
Development	3,164,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	73,000
Development Costs Transferred	1,187,000
Development costs incurred, for the period	1,977,000
Development cost incurred, cumulative	3,164,000
Estimated Total Cumulative Development Costs	5,000,000
Under construction [Member] | World Houston 31B, Houston, TX [Member]
Real estate properties component balance [Abstract]
Development	1,360,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	35,000
Development Costs Transferred	930,000
Development costs incurred, for the period	430,000
Development cost incurred, cumulative	1,360,000
Estimated Total Cumulative Development Costs	3,900,000
Under construction [Member] | Beltway Crossing IX, Houston, TX [Member]
Real estate properties component balance [Abstract]
Development	1,141,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	45,000
Development Costs Transferred	674,000
Development costs incurred, for the period	467,000
Development cost incurred, cumulative	1,141,000
Estimated Total Cumulative Development Costs	2,500,000
Under construction [Member] | Beltway Crossing X, Houston, TX [Member]
Real estate properties component balance [Abstract]
Development	2,006,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	78,000
Development Costs Transferred	1,183,000
Development costs incurred, for the period	823,000
Development cost incurred, cumulative	2,006,000
Estimated Total Cumulative Development Costs	4,500,000
Prospective Development [Member]
Real estate properties component balance [Abstract]
Development	81,455,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	5,896,000
Development Costs Transferred	(9,916,000)
Development costs incurred, for the period	20,111,000
Development cost incurred, cumulative	81,455,000
Estimated Total Cumulative Development Costs	382,200,000
Prospective Development [Member] | Tucson, AZ [Member]
Real estate properties component balance [Abstract]
Development	417,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	70,000
Development Costs Transferred	0
Development costs incurred, for the period	0
Development cost incurred, cumulative	417,000
Estimated Total Cumulative Development Costs	4,900,000
Prospective Development [Member] | Tampa, FL [Member]
Real estate properties component balance [Abstract]
Development	4,486,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	249,000
Development Costs Transferred	0
Development costs incurred, for the period	286,000
Development cost incurred, cumulative	4,486,000
Estimated Total Cumulative Development Costs	14,600,000
Prospective Development [Member] | Orlando, FL [Member]
Real estate properties component balance [Abstract]
Development	24,597,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	1,514,000
Development Costs Transferred	(1,987,000)
Development costs incurred, for the period	3,552,000
Development cost incurred, cumulative	24,597,000
Estimated Total Cumulative Development Costs	99,200,000
Prospective Development [Member] | Fort Myers, FL [Member]
Real estate properties component balance [Abstract]
Development	17,203,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	659,000
Development Costs Transferred	0
Development costs incurred, for the period	649,000
Development cost incurred, cumulative	17,203,000
Estimated Total Cumulative Development Costs	48,100,000
Prospective Development [Member] | Dallas, TX [Member]
Real estate properties component balance [Abstract]
Development	764,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	70,000
Development Costs Transferred	0
Development costs incurred, for the period	62,000
Development cost incurred, cumulative	764,000
Estimated Total Cumulative Development Costs	4,100,000
Prospective Development [Member] | El Paso, TX [Member]
Real estate properties component balance [Abstract]
Development	2,444,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	251,000
Development Costs Transferred	0
Development costs incurred, for the period	0
Development cost incurred, cumulative	2,444,000
Estimated Total Cumulative Development Costs	9,600,000
Prospective Development [Member] | Houston, TX [Member]
Real estate properties component balance [Abstract]
Development	21,115,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	2,044,000
Development Costs Transferred	(5,877,000)
Development costs incurred, for the period	11,594,000
Development cost incurred, cumulative	21,115,000
Estimated Total Cumulative Development Costs	129,600,000
Prospective Development [Member] | San Antonio, TX [Member]
Real estate properties component balance [Abstract]
Development	5,016,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	484,000
Development Costs Transferred	(2,052,000)
Development costs incurred, for the period	436,000
Development cost incurred, cumulative	5,016,000
Estimated Total Cumulative Development Costs	32,200,000
Prospective Development [Member] | Charlotte, NC [Member]
Real estate properties component balance [Abstract]
Development	1,246,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	95,000
Development Costs Transferred	0
Development costs incurred, for the period	71,000
Development cost incurred, cumulative	1,246,000
Estimated Total Cumulative Development Costs	7,100,000
Prospective Development [Member] | Jackson, MS [Member]
Real estate properties component balance [Abstract]
Development	706,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	28,000
Development Costs Transferred	0
Development costs incurred, for the period	0
Development cost incurred, cumulative	706,000
Estimated Total Cumulative Development Costs	2,000,000
Prospective Development [Member] | Phoenix, AZ [Member]
Real estate properties component balance [Abstract]
Development	3,461,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	432,000
Development Costs Transferred	0
Development costs incurred, for the period	3,461,000
Development cost incurred, cumulative	3,461,000
Estimated Total Cumulative Development Costs	30,800,000
Development completed and transferred to Real estate properties [Member]
Real estate properties component balance [Abstract]
Development	1,483,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	20,000
Development Costs Transferred	0
Development costs incurred, for the period	76,000
Development cost incurred, cumulative	1,483,000
Development completed and transferred to Real estate properties [Member] | Arion 8 Expansion, San Antonio, TX [Member]
Real estate properties component balance [Abstract]
Development	1,483,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	20,000
Development Costs Transferred	0
Development costs incurred, for the period	76,000
Development cost incurred, cumulative	1,483,000
Lease Up Construction And Prospective Development [Member]
Real estate properties component balance [Abstract]
Development	112,149,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	6,467,000
Development Costs Transferred	0
Development costs incurred, for the period	39,834,000
Development cost incurred, cumulative	112,149,000
Estimated Total Cumulative Development Costs	426,500,000
Development obligations	10,700,000
Tenant improvement obligations	2,000,000
Lease Up [Member]
Real estate properties component balance [Abstract]
Development	9,042,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	132,000.00
Development Costs Transferred	1,256,000
Development costs incurred, for the period	6,731,000
Development cost incurred, cumulative	9,042,000
Estimated Total Cumulative Development Costs	9,900,000
Lease Up [Member] | World Houston 31A, Houston, TX [Member]
Real estate properties component balance [Abstract]
Development	3,843,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	44,000.00
Development Costs Transferred	0
Development costs incurred, for the period	2,788,000
Development cost incurred, cumulative	3,843,000
Estimated Total Cumulative Development Costs	4,600,000
Lease Up [Member] | Beltway Crossing VIII, Houston, TX [Member]
Real estate properties component balance [Abstract]
Development	5,199,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	88,000.00
Development Costs Transferred	1,256,000
Development costs incurred, for the period	3,943,000
Development cost incurred, cumulative	5,199,000
Estimated Total Cumulative Development Costs	$ 5,300,000