MORTGAGE NOTES PAYABLE AND UNSECURED TERM LOAN PAYABLE (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Participating Mortgage Loans [Line Items]
Carrying Amount of Securing Real Estate	$ 582,898,000
Mortgage notes payable	607,766,000		628,170,000
Recourse liability	5,000,000
Unsecured Term Loans Payable [Abstract]
Effective interest rate (in hundredths)	2.01%		1.65%
Unsecured term loans	130,000,000		50,000,000
Payments of principal over the next five years [Abstract]
2013	57,915,000
2014	98,920,000
2015	102,287,000
2016	92,716,000
2017	58,145,000
$80 million Unsecured Term Loan [Member]
Unsecured Term Loans Payable [Abstract]
Effective interest rate (in hundredths)	2.92%	[1]
Debt Instrument, Maturity Date	Aug. 15, 2018	[1]
Unsecured term loans	80,000,000	[1]	0	[1]
Debt Instrument, Basis Spread on Variable Rate	1.90%
$50 Million Unsecured Term Loan [Member]
Unsecured Term Loans Payable [Abstract]
Effective interest rate (in hundredths)	3.91%
Debt Instrument, Maturity Date	Dec. 21, 2018
Unsecured term loans	50,000,000		50,000,000
University Business Center (120 and 130 Cremona) [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	6.43%
Monthly P & I Payment	81,856,000
Maturity Date	Repaid
Carrying Amount of Securing Real Estate	0
Mortgage notes payable	0		2,193,000
University Business Center (125 and 175 Cremona) [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	7.98%
Monthly P & I Payment	88,607,000
Maturity Date	Repaid
Carrying Amount of Securing Real Estate	0
Mortgage notes payable	0		8,771,000
Oak Creek Distribution Center IV [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	5.68%
Monthly P & I Payment	31,253,000
Maturity Date	Repaid
Carrying Amount of Securing Real Estate	0
Mortgage notes payable	0		3,506,000
Fifty First Avenue, Airport Distribution, Broadway I, III and IV, Chestnut, Interchange Business Park, Main Street, North Stemmons I land, Southpark, Southpointe, and World Houston 12 and 13 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	6.86%
Monthly P & I Payment	279,149,000
Maturity Date	Repaid
Carrying Amount of Securing Real Estate	0
Mortgage notes payable	0		32,204,000
Interstate Distribution Center - Jacksonville [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	5.64%
Monthly P & I Payment	31,645,000
Maturity Date	Repaid
Carrying Amount of Securing Real Estate	0
Mortgage notes payable	0		4,234,000
Thirty Fifth Avenue, Beltway I, Broadway V, Lockwood, Northwest Point, Sunbelt, Techway Southwest I and World Houston 10, 11 and 14 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	4.75%
Monthly P & I Payment	259,403,000
Maturity Date	9/5/2013
Carrying Amount of Securing Real Estate	37,775,000
Mortgage notes payable	34,474,000		35,912,000
Airport Commerce Center I and II, Interchange Park, Ridge Creek Distribution Center I, Southridge XII, Waterford Distribution Center and World Houston 24, 25 and 27 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	5.75%
Monthly P & I Payment	414,229,000
Maturity Date	1/5/2014
Carrying Amount of Securing Real Estate	64,794,000
Mortgage notes payable	52,086,000		54,001,000
Kyrene Distribution Center I [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	9.00%
Monthly P & I Payment	11,246,000
Maturity Date	7/1/2014
Carrying Amount of Securing Real Estate	2,095,000
Mortgage notes payable	198,000		310,000
Americas Ten I, Kirby, Palm River North I, II and III, Shady Trail, Westlake I and II and World Houston 17 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	5.68%
Monthly P & I Payment	175,479,000
Maturity Date	10/10/2014
Carrying Amount of Securing Real Estate	24,553,000
Mortgage notes payable	27,467,000		27,996,000
Beltway II, III and IV, Commerce Park 1, Eastlake, Fairgrounds I-IV, Nations Ford I-IV, Techway Southwest III, Wetmore I-IV and World Houston 15 and 22 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	5.50%
Monthly P & I Payment	536,552,000
Maturity Date	4/5/2015
Carrying Amount of Securing Real Estate	66,416,000
Mortgage notes payable	64,374,000		67,188,000
Country Club I, Lake Pointe, Techway Southwest II and World Houston 19 and 20 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	4.98%
Monthly P & I Payment	256,952,000
Maturity Date	12/5/2015
Carrying Amount of Securing Real Estate	20,777,000
Mortgage notes payable	29,465,000		31,039,000
Huntwood and Wiegman Distribution Centers [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	5.68%
Monthly P & I Payment	265,275,000
Maturity Date	9/5/2016
Carrying Amount of Securing Real Estate	21,343,000
Mortgage notes payable	30,332,000		31,748,000
Alamo Downs, Arion 1-15 and 17, Rampart I, II and III, Santan 10 and World Houston 16 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	5.97%
Monthly P & I Payment	557,467,000
Maturity Date	11/5/2016
Carrying Amount of Securing Real Estate	54,614,000
Mortgage notes payable	63,132,000		65,961,000
Arion 16, Broadway VI, Chino, East University I and II, Northpark I-IV, Santan 10 II, 55th Avenue and World Houston 1 and 2, 21 and 23 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	5.57%
Monthly P & I Payment	518,885,000
Maturity Date	9/5/2017
Carrying Amount of Securing Real Estate	54,998,000
Mortgage notes payable	60,310,000		63,093,000
Dominguez, Industry I and III, Kingsview, Shaw, Walnut and Washington [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	7.50%	[2]
Monthly P & I Payment	539,747,000	[2]
Maturity Date	5/5/2019	[2]
Carrying Amount of Securing Real Estate	48,301,000	[2]
Mortgage notes payable	61,052,000	[2]	62,875,000	[2]
Blue Heron Distribution Center II [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	5.39%
Monthly P & I Payment	16,176,000
Maturity Date	2/29/2020
Carrying Amount of Securing Real Estate	4,566,000
Mortgage notes payable	1,161,000		1,288,000
Fortieth Avenue, Beltway V, Centennial Park, Executive Airport, Ocean View, Techway Southwest IV, Wetmore V-VIII and World Houston 26, 28, 29 and 30 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	4.39%
Monthly P & I Payment	463,778,000
Maturity Date	1/5/2021
Carrying Amount of Securing Real Estate	74,918,000
Mortgage notes payable	69,376,000		71,837,000
America Plaza, Central Green, Glenmont I & II, Interstate I, II & III, Rojas, Stemmons Circle, Venture, West Loop I & II and World Houston 3-9 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	4.75%
Monthly P & I Payment	420,045,000
Maturity Date	6/5/2021
Carrying Amount of Securing Real Estate	46,047,000
Mortgage notes payable	61,970,000		64,014,000
Arion 18, Beltway VI & VII, Commerce Park II & III, Concord Distribution Center, Interstate Distribution Center V, VI & VII, Lakeview Business Center, Ridge Creek Distribution Center II, Southridge IV & V and World Houston 32 [Member]
Participating Mortgage Loans [Line Items]
Interest Rate (in hundredths)	4.09%
Monthly P & I Payment	329,796,000
Maturity Date	1/5/2022
Carrying Amount of Securing Real Estate	61,701,000
Mortgage notes payable	$ 52,369,000		$ 0

[1] The interest rate on this unsecured term loan is comprised of LIBOR plus 190 basis points subject to a pricing grid for changes in the Company's leverage or coverage ratings. The Company entered into an interest rate swap to convert the loan's LIBOR rate to a fixed interest rate, providing the Company an effective interest rate on the term loan of 2.92% as of December 31, 2012. See Note 13 for additional information on the interest rate swap.

[2] This mortgage loan has a recourse liability of $5 million which will be released based on the secured properties generating certain base rent amounts.