SECURED AND UNSECURED DEBT (Details)		12 Months Ended
		Dec. 31, 2015 USD ($) Decimal	Dec. 31, 2014 USD ($)
Secured and Unsecured Debt [Line Items]
Carrying Amount of Securing Real Estate		$ 359,347,000
Secured debt		351,401,000	$ 453,776,000
Recourse liability		5,000,000
Loans Payable, Noncurrent [Abstract]
Unsecured debt		530,000,000	380,000,000
Secured and unsecured debt [Member]
Payments of principal over the next five years [Abstract]
2016		92,804,000
2017		58,239,000
2018		141,316,000
2019		130,569,000
2020		$ 114,097,000
$80 million Unsecured Term Loan [Member]
Secured and Unsecured Debt [Line Items]
Debt instrument, spread above LIBOR variable rate (in basis points) | Decimal		175
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)	[1]	2.77%
Debt Instrument, Maturity Date	[1]	Aug. 15, 2018
Unsecured debt	[1]	$ 80,000,000	80,000,000
$50 Million Unsecured Term Loan [Member]
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)		3.91%
Debt Instrument, Maturity Date		Dec. 21, 2018
Unsecured debt		$ 50,000,000	50,000,000
Seventy-Five Million Unsecured Term Loan (closed in 2014) [Member]
Secured and Unsecured Debt [Line Items]
Debt instrument, spread above LIBOR variable rate (in basis points) | Decimal		115
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)	[2]	2.846%
Debt Instrument, Maturity Date	[2]	Jul. 31, 2019
Unsecured debt	[2]	$ 75,000,000	75,000,000
$75 Million Unsecured Term Loan [Member]
Secured and Unsecured Debt [Line Items]
Debt instrument, spread above LIBOR variable rate (in basis points) | Decimal		140
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)	[3]	3.752%
Debt Instrument, Maturity Date	[3]	Dec. 20, 2020
Unsecured debt	[3]	$ 75,000,000	75,000,000
Seventy-Five Million Unsecured Term Loan executed in 2015 [Member]
Secured and Unsecured Debt [Line Items]
Debt instrument, spread above LIBOR variable rate (in basis points) | Decimal		140
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)	[4]	3.031%
Debt Instrument, Maturity Date	[4]	Feb. 28, 2022
Unsecured debt	[4]	$ 75,000,000	0
Thirty million senior unsecured notes [Member]
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)		3.80%
Debt Instrument, Maturity Date		Aug. 28, 2020
Unsecured debt		$ 30,000,000	30,000,000
Fifty million senior unsecured notes [Member]
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)		3.80%
Debt Instrument, Maturity Date		Aug. 28, 2023
Unsecured debt		$ 50,000,000	50,000,000
Twenty million senior unsecured notes [Member]
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)		3.80%
Debt Instrument, Maturity Date		Aug. 28, 2025
Unsecured debt		$ 20,000,000	20,000,000
Twenty-five million senior unsecured notes (executed in 2015) [Member]
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)		3.97%
Debt Instrument, Maturity Date		Oct. 01, 2025
Unsecured debt		$ 25,000,000	0
Fifty million senior unsecured notes (executed in 2015) [Member]
Loans Payable, Noncurrent [Abstract]
Effective interest rate (in hundredths)		3.99%
Debt Instrument, Maturity Date		Oct. 07, 2025
Unsecured debt		$ 50,000,000	0
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]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		5.50%
Monthly P & I Payment		$ 536,552
Carrying Amount of Securing Real Estate		0
Secured debt		$ 0	58,262,000
Country Club I, Lake Pointe, Techway Southwest II and World Houston 19 and 20 [Member]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		4.98%
Monthly P & I Payment		$ 256,952
Carrying Amount of Securing Real Estate		0
Secured debt		$ 0	26,074,000
Huntwood and Wiegman I-IV Distribution Centers [Member]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		5.68%
Monthly P & I Payment		$ 265,275
Maturity Date		9/5/2016
Carrying Amount of Securing Real Estate		$ 19,991,000
Secured debt		$ 25,567,000	27,246,000
Alamo Downs, Arion 1-15 and 17, Rampart I, II, III & IV, Santan 10 and World Houston 16 [Member]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		5.97%
Monthly P & I Payment		$ 557,467
Maturity Date		10/5/2016
Carrying Amount of Securing Real Estate		$ 57,654,000
Secured debt		$ 53,563,000	56,945,000
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]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		5.57%
Monthly P & I Payment		$ 518,885
Maturity Date		9/5/2017
Carrying Amount of Securing Real Estate		$ 49,692,000
Secured debt		$ 50,971,000	54,259,000
Dominguez, Industry I and III, Kingsview, Shaw, Walnut and Washington [Member]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)	[5]	7.50%
Monthly P & I Payment	[5]	$ 539,747
Maturity Date	[5]	5/5/2019
Carrying Amount of Securing Real Estate	[5]	$ 47,123,000
Secured debt	[5]	$ 54,689,000	56,970,000
Blue Heron Distribution Center II [Member]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		5.39%
Monthly P & I Payment		$ 16,176
Maturity Date		2/29/2020
Carrying Amount of Securing Real Estate		$ 4,174,000
Secured debt		$ 735,000	884,000
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]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		4.39%
Monthly P & I Payment		$ 463,778
Maturity Date		1/5/2021
Carrying Amount of Securing Real Estate		$ 68,092,000
Secured debt		$ 61,312,000	64,119,000
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]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		4.75%
Monthly P & I Payment		$ 420,045
Maturity Date		6/5/2021
Carrying Amount of Securing Real Estate		$ 43,369,000
Secured debt		$ 55,223,000	57,579,000
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]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		4.09%
Monthly P & I Payment		$ 329,796
Maturity Date		1/5/2022
Carrying Amount of Securing Real Estate		$ 59,908,000
Secured debt		$ 46,584,000	48,592,000
Ramona Distribution Center [Member]
Secured and Unsecured Debt [Line Items]
Interest Rate (in hundredths)		3.85%
Monthly P & I Payment		$ 16,287
Maturity Date		11/30/2026
Carrying Amount of Securing Real Estate		$ 9,344,000
Secured debt		$ 2,757,000	$ 2,846,000

[1] The interest rate on this unsecured term loan is comprised of LIBOR plus 175 basis points subject to a pricing grid for changes in the Company's 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 2.770% as of December 31, 2015. See Note 13 for additional information on the interest rate swap.

[2] The interest rate on this unsecured term loan is comprised of LIBOR plus 115 basis points subject to a pricing grid for changes in the Company's 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 a weighted average effective interest rate on the term loan of 2.846% as of December 31, 2015. See Note 13 for additional information on the interest rate swap.

[3] The interest rate on this unsecured term loan is comprised of LIBOR plus 140 basis points subject to a pricing grid for changes in the Company's coverage ratings. The Company entered into two interest rate swaps to convert the loan's LIBOR rate to a fixed interest rate, providing the Company a weighted average effective interest rate on the term loan of 3.752% as of December 31, 2015. See Note 13 for additional information on the interest rate swaps.

[4] The interest rate on this unsecured term loan is comprised of LIBOR plus 140 basis points subject to a pricing grid for changes in the Company's 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 a weighted average effective interest rate on the term loan of 3.031% as of December 31, 2015. See Note 13 for additional information on the interest rate swap.

[5] This mortgage loan has a recourse liability of $5.0 million which will be released based on the secured properties generating certain base rent amounts.