REAL ESTATE PROPERTIES (Details) (USD $)	3 Months Ended									12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Real Estate [Abstract]
Land	$ 244,199,000					$ 235,394,000				$ 244,199,000		$ 235,394,000
Buildings and building improvements	1,102,597,000					1,056,783,000				1,102,597,000		1,056,783,000
Tenant and other improvements	272,981,000					258,267,000				272,981,000		258,267,000
Development	148,255,000					112,149,000				148,255,000		112,149,000
Real estate and development properties	1,768,032,000					1,662,593,000				1,768,032,000		1,662,593,000
Less accumulated depreciation	(496,247,000)					(451,805,000)				(496,247,000)		(451,805,000)
Real estate, net	1,271,785,000					1,210,788,000				1,271,785,000		1,210,788,000
Real Estate Property Sales [Abstract]
Net Sales Price										17,087,000
Basis										10,577,000
Recognized Gain										6,510,000
Deferred gain recognized in current period from previous period sales												36,000		37,000
Discontinued Operations [Abstract]
Income from real estate operations										1,403,000		1,463,000		1,115,000
Expenses from real estate operations										(346,000)		(498,000)		(463,000)
Property net operating income from discontinued operations										1,057,000		965,000		652,000
Other income										0		5,000		42,000
Depreciation and amortization										(578,000)		(694,000)		(544,000)
Income from real estate operations										479,000		276,000		150,000
Gain on sales of nondepreciable real estate investments, net of tax										167,000	[1]	0	[1]	0	[1]
Gain on sales of real estate investments										6,343,000		0		0
INCOME FROM DISCONTINUED OPERATIONS	4,592,000		133,000	2,004,000	261,000	86,000	80,000	72,000	38,000	6,989,000		276,000		150,000
DEVELOPMENT [Abstract]
Development costs incurred, for the period										55,404,000		42,148,000		9,145,000
Development	148,255,000					112,149,000				148,255,000		112,149,000
Interest costs capitalized on development properties										4,660,000		3,771,000		3,613,000
Internal Development Costs Capitalized During Period										2,810,000		1,334,000		302,000
Improvements on developments transferred to real estate properties										1,338,000
Future Minimum payments receivable [Abstract]
2013	137,081,000									137,081,000
2014	110,073,000									110,073,000
2015	81,752,000									81,752,000
2016	55,304,000									55,304,000
2017	36,811,000									36,811,000
Thereafter	55,985,000									55,985,000
Total minimum receipts	477,006,000									477,006,000
Tulsa, OK [Member]
Real Estate Property Sales [Abstract]
Size of property sold (in square feet)										259,000
Date of property sale										12/27/2012
Net Sales Price										9,688,000
Basis										5,214,000
Recognized Gain										4,474,000
Phoenix, AZ [Member]
Real Estate Property Sales [Abstract]
Size of property sold (in square feet)										174,000
Date of property sale										6/13/2012
Net Sales Price										6,861,000
Basis										4,992,000
Recognized Gain										1,869,000
Tampa, FL [Member]
Real Estate Property Sales [Abstract]
Size of property sold (in square feet)										10,500
Date of property sale										2/15/2012
Net Sales Price										538,000
Basis										371,000
Recognized Gain										167,000
Lease Up [Member]
Real Estate [Abstract]
Development	26,880,000									26,880,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	386,000									386,000
Development Costs Transferred										2,298,000	[2]
Development costs incurred, for the period										10,281,000
Development	26,880,000									26,880,000
Estimated Total Cumulative Development Costs										31,800,000	[3]
Lease Up [Member] | Southridge IX, Orlando, FL [Member]
Real Estate [Abstract]
Development	6,300,000									6,300,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	76,000									76,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										938,000
Development	6,300,000									6,300,000
Estimated Total Cumulative Development Costs										7,100,000	[3]
Lease Up [Member] | World Houston 31B, Houston, TX [Member]
Real Estate [Abstract]
Development	2,951,000									2,951,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	35,000									35,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,591,000
Development	2,951,000									2,951,000
Estimated Total Cumulative Development Costs										3,900,000	[3]
Lease Up [Member] | Thousand Oaks 1, San Antonio, TX [Member]
Real Estate [Abstract]
Development	3,539,000									3,539,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	36,000									36,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,130,000
Development	3,539,000									3,539,000
Estimated Total Cumulative Development Costs										4,700,000	[3]
Lease Up [Member] | Thousand Oaks 2, San Antonio, TX [Member]
Real Estate [Abstract]
Development	4,809,000									4,809,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	73,000									73,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,645,000
Development	4,809,000									4,809,000
Estimated Total Cumulative Development Costs										5,600,000	[3]
Lease Up [Member] | Beltway Crossing X, Houston, TX [Member]
Real Estate [Abstract]
Development	3,816,000									3,816,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	78,000									78,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,810,000
Development	3,816,000									3,816,000
Estimated Total Cumulative Development Costs										4,300,000	[3]
Lease Up [Member] | Southridge XI, Orlando, FL [Member]
Real Estate [Abstract]
Development	5,465,000									5,465,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	88,000									88,000
Development Costs Transferred										2,298,000	[2]
Development costs incurred, for the period										3,167,000
Development	5,465,000									5,465,000
Estimated Total Cumulative Development Costs										6,200,000	[3]
Under construction [Member]
Real Estate [Abstract]
Development	24,542,000									24,542,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	669,000									669,000
Development Costs Transferred										8,532,000	[2]
Development costs incurred, for the period										16,010,000
Development	24,542,000									24,542,000
Estimated Total Cumulative Development Costs										48,600,000	[3]
Under construction [Member] | Beltway Crossing XI, Houston, TX [Member]
Real Estate [Abstract]
Development	3,600,000									3,600,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	87,000									87,000
Development Costs Transferred										1,184,000	[2]
Development costs incurred, for the period										2,416,000
Development	3,600,000									3,600,000
Estimated Total Cumulative Development Costs										4,900,000	[3]
Under construction [Member] | World Houston 33, Houston, TX [Member]
Real Estate [Abstract]
Development	9,084,000									9,084,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	160,000									160,000
Development Costs Transferred										1,338,000	[2]
Development costs incurred, for the period										7,746,000
Development	9,084,000									9,084,000
Estimated Total Cumulative Development Costs										10,900,000	[3]
Under construction [Member] | World Houston 34, Houston, TX [Member]
Real Estate [Abstract]
Development	2,675,000									2,675,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	57,000									57,000
Development Costs Transferred										1,039,000	[2]
Development costs incurred, for the period										1,636,000
Development	2,675,000									2,675,000
Estimated Total Cumulative Development Costs										3,600,000	[3]
Under construction [Member] | World Houston 35, Houston, TX [Member]
Real Estate [Abstract]
Development	2,113,000									2,113,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	45,000									45,000
Development Costs Transferred										806,000	[2]
Development costs incurred, for the period										1,307,000
Development	2,113,000									2,113,000
Estimated Total Cumulative Development Costs										2,800,000	[3]
Under construction [Member] | Ten West Crossing 1, Houston, TX [Member]
Real Estate [Abstract]
Development	1,742,000									1,742,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	30,000									30,000
Development Costs Transferred										423,000	[2]
Development costs incurred, for the period										1,319,000
Development	1,742,000									1,742,000
Estimated Total Cumulative Development Costs										3,800,000	[3]
Under construction [Member] | World Houston 36, Houston, TX [Member]
Real Estate [Abstract]
Development	1,437,000									1,437,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	60,000									60,000
Development Costs Transferred										986,000	[2]
Development costs incurred, for the period										451,000
Development	1,437,000									1,437,000
Estimated Total Cumulative Development Costs										6,100,000	[3]
Under construction [Member] | World Houston 37, Houston, TX [Member]
Real Estate [Abstract]
Development	1,674,000									1,674,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	101,000									101,000
Development Costs Transferred										1,233,000	[2]
Development costs incurred, for the period										441,000
Development	1,674,000									1,674,000
Estimated Total Cumulative Development Costs										7,100,000	[3]
Under construction [Member] | World Houston 38, Houston, TX [Member]
Real Estate [Abstract]
Development	2,217,000									2,217,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	129,000									129,000
Development Costs Transferred										1,523,000	[2]
Development costs incurred, for the period										694,000
Development	2,217,000									2,217,000
Estimated Total Cumulative Development Costs										9,400,000	[3]
Prospective Development [Member]
Real Estate [Abstract]
Development	96,833,000									96,833,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	6,603,000									6,603,000
Development Costs Transferred										(10,830,000)	[2]
Development costs incurred, for the period										26,208,000
Development	96,833,000									96,833,000
Estimated Total Cumulative Development Costs										441,800,000	[3]
Prospective Development [Member] | Phoenix, AZ [Member]
Real Estate [Abstract]
Development	5,697,000									5,697,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	528,000									528,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										2,236,000
Development	5,697,000									5,697,000
Estimated Total Cumulative Development Costs										40,100,000	[3]
Prospective Development [Member] | Tucson, AZ [Member]
Real Estate [Abstract]
Development	417,000									417,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	70,000									70,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										0
Development	417,000									417,000
Estimated Total Cumulative Development Costs										4,900,000	[3]
Prospective Development [Member] | Denver, CO [Member]
Real Estate [Abstract]
Development	711,000									711,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	84,000									84,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										711,000
Development	711,000									711,000
Estimated Total Cumulative Development Costs										7,700,000	[3]
Prospective Development [Member] | Fort Myers, FL [Member]
Real Estate [Abstract]
Development	17,646,000									17,646,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	663,000									663,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										443,000
Development	17,646,000									17,646,000
Estimated Total Cumulative Development Costs										48,100,000	[3]
Prospective Development [Member] | Orlando, FL [Member]
Real Estate [Abstract]
Development	26,600,000									26,600,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	1,426,000									1,426,000
Development Costs Transferred										(2,298,000)	[2]
Development costs incurred, for the period										4,301,000
Development	26,600,000									26,600,000
Estimated Total Cumulative Development Costs										93,100,000	[3]
Prospective Development [Member] | Tampa, FL [Member]
Real Estate [Abstract]
Development	6,145,000									6,145,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	519,000									519,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,659,000
Development	6,145,000									6,145,000
Estimated Total Cumulative Development Costs										30,800,000	[3]
Prospective Development [Member] | Jackson, MS [Member]
Real Estate [Abstract]
Development	706,000									706,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	28,000									28,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										0
Development	706,000									706,000
Estimated Total Cumulative Development Costs										2,000,000	[3]
Prospective Development [Member] | Charlotte, NC [Member]
Real Estate [Abstract]
Development	1,335,000									1,335,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	95,000									95,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										89,000
Development	1,335,000									1,335,000
Estimated Total Cumulative Development Costs										6,800,000	[3]
Prospective Development [Member] | Dallas, TX [Member]
Real Estate [Abstract]
Development	1,235,000									1,235,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	120,000									120,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										471,000
Development	1,235,000									1,235,000
Estimated Total Cumulative Development Costs										7,800,000	[3]
Prospective Development [Member] | El Paso, TX [Member]
Real Estate [Abstract]
Development	2,444,000									2,444,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	251,000									251,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										0
Development	2,444,000									2,444,000
Estimated Total Cumulative Development Costs										11,300,000	[3]
Prospective Development [Member] | Houston, TX [Member]
Real Estate [Abstract]
Development	28,433,000									28,433,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	2,341,000									2,341,000
Development Costs Transferred										(8,532,000)	[2]
Development costs incurred, for the period										15,850,000
Development	28,433,000									28,433,000
Estimated Total Cumulative Development Costs										157,400,000	[3]
Prospective Development [Member] | San Antonio, TX [Member]
Real Estate [Abstract]
Development	5,464,000									5,464,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	478,000									478,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										448,000
Development	5,464,000									5,464,000
Estimated Total Cumulative Development Costs										31,800,000	[3]
Development completed and transferred to Real estate properties [Member]
Real Estate [Abstract]
Development	17,960,000	[4]								17,960,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	273,000									273,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,567,000
Development	17,960,000	[4]								17,960,000	[4]
Development completed and transferred to Real estate properties [Member] | Beltway Crossing VIII, Houston, TX [Member]
Real Estate [Abstract]
Development	5,242,000									5,242,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	88,000									88,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										43,000
Development	5,242,000									5,242,000
Development completed and transferred to Real estate properties [Member] | World Houston 32, Houston, TX [Member]
Real Estate [Abstract]
Development	6,276,000									6,276,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	96,000									96,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										66,000
Development	6,276,000									6,276,000
Development completed and transferred to Real estate properties [Member] | World Houston 31A, Houston, TX [Member]
Real Estate [Abstract]
Development	4,086,000									4,086,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	44,000									44,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										243,000
Development	4,086,000									4,086,000
Development completed and transferred to Real estate properties [Member] | Beltway Crossing IX, Houston, TX [Member]
Real Estate [Abstract]
Development	2,356,000									2,356,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	45,000									45,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,215,000
Development	2,356,000									2,356,000
Lease Up Construction And Prospective Development [Member]
Real Estate [Abstract]
Development	148,255,000									148,255,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	7,658,000									7,658,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										52,499,000
Development	148,255,000									148,255,000
Estimated Total Cumulative Development Costs										522,200,000	[3]
Development obligations	20,400,000									20,400,000
Tenant improvement obligations										6,100,000
Tampa East Distribution Center III and Tampa West Distribution Center VIII [Member]
Discontinued Operations [Abstract]
Tax on gain of property sold										$ 6,000

[1] Gains on sales of nondepreciable real estate investments are subject to federal and state taxes. The Company recognized taxes of $6,000 on the gains related to the sales of Tampa East Distribution Center III and Tampa West Distribution Center VIII during 2012.

[2] Represents costs transferred from Prospective Development (primarily land) to Under Construction during the period.

[3] Included in these costs are development obligations of $20.4 million and tenant improvement obligations of $6.1 million on properties under development.

[4] Represents cumulative costs at the date of transfer.