REAL ESTATE PROPERTIES (Details) (USD $)	3 Months Ended									12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Real Estate [Abstract]
Land	$ 265,871,000					$ 244,199,000				$ 265,871,000		$ 244,199,000
Buildings and building improvements	1,210,318,000					1,102,597,000				1,210,318,000		1,102,597,000
Tenant and other improvements	302,370,000					272,981,000				302,370,000		272,981,000
Development	148,767,000					148,255,000				148,767,000		148,255,000
Real estate and development properties	1,927,326,000					1,768,032,000				1,927,326,000		1,768,032,000
Less accumulated depreciation	(550,113,000)					(496,247,000)				(550,113,000)		(496,247,000)
Real estate, net	1,377,213,000					1,271,785,000				1,377,213,000		1,271,785,000
Real Estate Property Sales [Abstract]
Net Sales Price										2,960,000		17,087,000
Basis										2,162,000		10,577,000
Recognized Gain										798,000		6,510,000
Deferred gain recognized in current period from previous period sales														36,000
Discontinued Operations [Abstract]
Income from real estate operations										306,000		1,737,000		1,475,000
Expenses from real estate operations										(87,000)		(448,000)		(499,000)
Property net operating income from discontinued operations										219,000		1,289,000		976,000
Other income										0		0		5,000
Depreciation and amortization										(130,000)		(929,000)		(712,000)
Income from real estate operations										89,000		360,000		269,000
Gain on sales of nondepreciable real estate investments										0	[1]	167,000	[1]	0	[1]
Gain on sales of real estate investments										798,000		6,343,000		0
INCOME FROM DISCONTINUED OPERATIONS	832,000		19,000	35,000	1,000	4,572,000	104,000	1,970,000	225,000	887,000		6,870,000		269,000
DEVELOPMENT [Abstract]
Development costs incurred, for the period										76,240,000		55,404,000		42,148,000
Development	148,767,000					148,255,000				148,767,000		148,255,000
Interest costs capitalized on development properties										5,064,000		4,660,000		3,771,000
Internal Development Costs Capitalized During Period										3,730,000		2,810,000		1,334,000
Improvements on developments transferred to real estate properties										4,497,000
Future Minimum payments receivable [Abstract]
2014	155,016,000									155,016,000
2015	126,497,000									126,497,000
2016	91,403,000									91,403,000
2017	64,542,000									64,542,000
2018	43,663,000									43,663,000
Thereafter	82,068,000									82,068,000
Total minimum receipts	563,189,000									563,189,000
Lease Up [Member]
Real Estate [Abstract]
Development	25,995,000									25,995,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	407,000									407,000
Development Costs Transferred										4,644,000	[2]
Development costs incurred, for the period										19,677,000
Development	25,995,000									25,995,000
Estimated Total Cumulative Development Costs										31,600,000	[3]
Under construction [Member]
Real Estate [Abstract]
Development	23,166,000									23,166,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	800,000									800,000
Development Costs Transferred										9,260,000	[2]
Development costs incurred, for the period										13,906,000
Development	23,166,000									23,166,000
Estimated Total Cumulative Development Costs										55,800,000	[3]
Prospective Development [Member]
Real Estate [Abstract]
Development	99,606,000									99,606,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	6,109,000									6,109,000
Development Costs Transferred										(15,883,000)	[2]
Development costs incurred, for the period										18,656,000
Development	99,606,000									99,606,000
Estimated Total Cumulative Development Costs										417,500,000	[3]
Prospective Development [Member] | Phoenix Area [Member]
Real Estate [Abstract]
Development	4,373,000									4,373,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	406,000									406,000
Development Costs Transferred										(1,811,000)	[2]
Development costs incurred, for the period										487,000
Development	4,373,000									4,373,000
Estimated Total Cumulative Development Costs										30,800,000	[3]
Prospective Development [Member] | Tucson [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	0									0
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	0									0
Development Costs Transferred										(977,000)	[2]
Development costs incurred, for the period										266,000
Development	0									0
Estimated Total Cumulative Development Costs										0	[3]
Prospective Development [Member] | Fort Myers [Member]
Real Estate [Abstract]
Development	17,858,000									17,858,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	663,000									663,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										212,000
Development	17,858,000									17,858,000
Estimated Total Cumulative Development Costs										50,000,000	[3]
Prospective Development [Member] | Orlando [Member]
Real Estate [Abstract]
Development	24,674,000									24,674,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	1,267,000									1,267,000
Development Costs Transferred										(4,157,000)	[2]
Development costs incurred, for the period										2,231,000
Development	24,674,000									24,674,000
Estimated Total Cumulative Development Costs										91,200,000	[3]
Prospective Development [Member] | Tampa [Member]
Real Estate [Abstract]
Development	6,822,000									6,822,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	519,000									519,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										677,000
Development	6,822,000									6,822,000
Estimated Total Cumulative Development Costs										31,100,000	[3]
Prospective Development [Member] | Jackson area [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 [Member]
Real Estate [Abstract]
Development	7,354,000									7,354,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	418,000									418,000
Development Costs Transferred										(1,789,000)	[2]
Development costs incurred, for the period										7,808,000
Development	7,354,000									7,354,000
Estimated Total Cumulative Development Costs										29,800,000	[3]
Prospective Development [Member] | Dallas [Member]
Real Estate [Abstract]
Development	1,249,000									1,249,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	120,000									120,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										14,000
Development	1,249,000									1,249,000
Estimated Total Cumulative Development Costs										7,800,000	[3]
Prospective Development [Member] | El Paso [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 [Member]
Real Estate [Abstract]
Development	28,159,000									28,159,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	1,889,000									1,889,000
Development Costs Transferred										(5,917,000)	[2]
Development costs incurred, for the period										5,643,000
Development	28,159,000									28,159,000
Estimated Total Cumulative Development Costs										126,400,000	[3]
Prospective Development [Member] | San Antonio [Member]
Real Estate [Abstract]
Development	5,550,000									5,550,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	478,000									478,000
Development Costs Transferred										(1,232,000)	[2]
Development costs incurred, for the period										1,318,000
Development	5,550,000									5,550,000
Estimated Total Cumulative Development Costs										32,200,000	[3]
Development completed and transferred to Real estate properties [Member]
Real Estate [Abstract]
Development	69,943,000	[4]								69,943,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	1,025,000									1,025,000
Development Costs Transferred										1,979,000	[2]
Development costs incurred, for the period										18,216,000
Development	69,943,000	[4]								69,943,000	[4]
Development completed and transferred to Real estate properties [Member] | Southridge IX [Member]
Real Estate [Abstract]
Development	6,318,000	[4]								6,318,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	76,000									76,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										18,000
Development	6,318,000	[4]								6,318,000	[4]
Completion date (or anticipated completion date, if under construction)										03/12
Development completed and transferred to Real estate properties [Member] | Southridge XI [Member]
Real Estate [Abstract]
Development	5,502,000	[4]								5,502,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	88,000									88,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										37,000
Development	5,502,000	[4]								5,502,000	[4]
Completion date (or anticipated completion date, if under construction)										09/12
Development completed and transferred to Real estate properties [Member] | World Houston 33 [Member]
Real Estate [Abstract]
Development	8,915,000	[4]								8,915,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	160,000									160,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										(169,000)
Development	8,915,000	[4]								8,915,000	[4]
Completion date (or anticipated completion date, if under construction)										02/13
Development completed and transferred to Real estate properties [Member] | World Houston Intl Business Ctr 31B [Member]
Real Estate [Abstract]
Development	3,026,000	[4]								3,026,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	35,000									35,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										75,000
Development	3,026,000	[4]								3,026,000	[4]
Completion date (or anticipated completion date, if under construction)										04/12
Development completed and transferred to Real estate properties [Member] | Ten West Crossing 1 [Member]
Real Estate [Abstract]
Development	3,144,000	[4]								3,144,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	30,000									30,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,402,000
Development	3,144,000	[4]								3,144,000	[4]
Completion date (or anticipated completion date, if under construction)										04/13
Development completed and transferred to Real estate properties [Member] | Thousand Oaks I [Member]
Real Estate [Abstract]
Development	3,993,000	[4]								3,993,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	36,000									36,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										454,000
Development	3,993,000	[4]								3,993,000	[4]
Completion date (or anticipated completion date, if under construction)										05/12
Development completed and transferred to Real estate properties [Member] | Thousand Oaks 2 [Member]
Real Estate [Abstract]
Development	5,322,000	[4]								5,322,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	73,000									73,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										513,000
Development	5,322,000	[4]								5,322,000	[4]
Completion date (or anticipated completion date, if under construction)										05/12
Development completed and transferred to Real estate properties [Member] | Beltway Crossing X [Member]
Real Estate [Abstract]
Development	4,196,000	[4]								4,196,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	79,000									79,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										380,000
Development	4,196,000	[4]								4,196,000	[4]
Completion date (or anticipated completion date, if under construction)										06/12
Development completed and transferred to Real estate properties [Member] | World Houston 34 [Member]
Real Estate [Abstract]
Development	3,733,000	[4]								3,733,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	57,000									57,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,058,000
Development	3,733,000	[4]								3,733,000	[4]
Completion date (or anticipated completion date, if under construction)										04/13
Development completed and transferred to Real estate properties [Member] | World Houston 35 [Member]
Real Estate [Abstract]
Development	2,691,000	[4]								2,691,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	45,000									45,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										578,000
Development	2,691,000	[4]								2,691,000	[4]
Completion date (or anticipated completion date, if under construction)										04/13
Development completed and transferred to Real estate properties [Member] | World Houston 36 [Member]
Real Estate [Abstract]
Development	5,309,000	[4]								5,309,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	60,000									60,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										3,872,000
Development	5,309,000	[4]								5,309,000	[4]
Completion date (or anticipated completion date, if under construction)										09/13
Development completed and transferred to Real estate properties [Member] | Southridge X [Member]
Real Estate [Abstract]
Development	5,181,000	[4]								5,181,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	71,000									71,000
Development Costs Transferred										1,979,000	[2]
Development costs incurred, for the period										3,202,000
Development	5,181,000	[4]								5,181,000	[4]
Completion date (or anticipated completion date, if under construction)										09/13
Development completed and transferred to Real estate properties [Member] | World Houston 38 [Member]
Real Estate [Abstract]
Development	7,830,000	[4]								7,830,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	128,000									128,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										5,613,000
Development	7,830,000	[4]								7,830,000	[4]
Completion date (or anticipated completion date, if under construction)										10/13
Development completed and transferred to Real estate properties [Member] | Beltway Crossing XI [Member]
Real Estate [Abstract]
Development	4,783,000	[4]								4,783,000	[4]
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	87,000									87,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										1,183,000
Development	4,783,000	[4]								4,783,000	[4]
Completion date (or anticipated completion date, if under construction)										02/13
Lease Up Construction And Prospective Development [Member]
Real Estate [Abstract]
Development	148,767,000									148,767,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	7,316,000									7,316,000
Development Costs Transferred										(1,979,000)	[2]
Development costs incurred, for the period										52,239,000
Development	148,767,000									148,767,000
Estimated Total Cumulative Development Costs										504,900,000	[3]
Development obligations	19,800,000									19,800,000
Tenant improvement obligations	6,600,000									6,600,000
Tampa East Distribution Center III and Tampa West Distribution Center VIII [Member]
Discontinued Operations [Abstract]
Tax on gain of property sold												6,000
Thousand Oaks 3 [Member] | Lease Up [Member]
Real Estate [Abstract]
Development	4,300,000									4,300,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	66,000									66,000
Development Costs Transferred										1,232,000	[2]
Development costs incurred, for the period										3,068,000
Development	4,300,000									4,300,000
Estimated Total Cumulative Development Costs										5,000,000	[3]
Completion date (or anticipated completion date, if under construction)										07/13
Ten West Crossing 2 [Member] | Lease Up [Member]
Real Estate [Abstract]
Development	4,089,000									4,089,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	46,000									46,000
Development Costs Transferred										908,000	[2]
Development costs incurred, for the period										3,181,000
Development	4,089,000									4,089,000
Estimated Total Cumulative Development Costs										5,300,000	[3]
Completion date (or anticipated completion date, if under construction)										09/13
Ten West Crossing 3 [Member] | Lease Up [Member]
Real Estate [Abstract]
Development	4,369,000									4,369,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	68,000									68,000
Development Costs Transferred										693,000	[2]
Development costs incurred, for the period										3,676,000
Development	4,369,000									4,369,000
Estimated Total Cumulative Development Costs										5,300,000	[3]
Completion date (or anticipated completion date, if under construction)										09/13
World Houston 37, Houston, TX [Member] | Lease Up [Member]
Real Estate [Abstract]
Development	5,379,000									5,379,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	101,000									101,000
Development Costs Transferred										0	[2]
Development costs incurred, for the period										3,705,000
Development	5,379,000									5,379,000
Estimated Total Cumulative Development Costs										7,100,000	[3]
Completion date (or anticipated completion date, if under construction)										09/13
Chandler Freeways [Member] | Lease Up [Member]
Real Estate [Abstract]
Development	7,858,000									7,858,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	126,000									126,000
Development Costs Transferred										1,811,000	[2]
Development costs incurred, for the period										6,047,000
Development	7,858,000									7,858,000
Estimated Total Cumulative Development Costs										8,900,000	[3]
Completion date (or anticipated completion date, if under construction)										11/13
Horizon I [Member] | Under construction [Member]
Real Estate [Abstract]
Development	5,301,000									5,301,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	109,000									109,000
Development Costs Transferred										2,178,000	[2]
Development costs incurred, for the period										3,123,000
Development	5,301,000									5,301,000
Estimated Total Cumulative Development Costs										7,700,000	[3]
Completion date (or anticipated completion date, if under construction)										02/14
Steele Creek I [Member] | Under construction [Member]
Real Estate [Abstract]
Development	4,267,000									4,267,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	71,000									71,000
Development Costs Transferred										895,000	[2]
Development costs incurred, for the period										3,372,000
Development	4,267,000									4,267,000
Estimated Total Cumulative Development Costs										5,300,000	[3]
Completion date (or anticipated completion date, if under construction)										02/14
Steele Creek II [Member] | Under construction [Member]
Real Estate [Abstract]
Development	3,341,000									3,341,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	71,000									71,000
Development Costs Transferred										894,000	[2]
Development costs incurred, for the period										2,447,000
Development	3,341,000									3,341,000
Estimated Total Cumulative Development Costs										5,300,000	[3]
Completion date (or anticipated completion date, if under construction)										02/14
Ten West Crossing 4 [Member] | Under construction [Member]
Real Estate [Abstract]
Development	3,461,000									3,461,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	68,000									68,000
Development Costs Transferred										927,000	[2]
Development costs incurred, for the period										2,534,000
Development	3,461,000									3,461,000
Estimated Total Cumulative Development Costs										4,800,000	[3]
Completion date (or anticipated completion date, if under construction)										02/14
World Houston 39 [Member] | Under construction [Member]
Real Estate [Abstract]
Development	1,636,000									1,636,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	94,000									94,000
Development Costs Transferred										922,000	[2]
Development costs incurred, for the period										714,000
Development	1,636,000									1,636,000
Estimated Total Cumulative Development Costs										5,700,000	[3]
Completion date (or anticipated completion date, if under construction)										05/14
Rampart IV [Member] | Under construction [Member]
Real Estate [Abstract]
Development	1,718,000									1,718,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	84,000									84,000
Development Costs Transferred										977,000	[2]
Development costs incurred, for the period										741,000
Development	1,718,000									1,718,000
Estimated Total Cumulative Development Costs										8,300,000	[3]
Completion date (or anticipated completion date, if under construction)										06/14
Ten West Crossing 5 [Member] | Under construction [Member]
Real Estate [Abstract]
Development	1,412,000									1,412,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	101,000									101,000
Development Costs Transferred										1,113,000	[2]
Development costs incurred, for the period										299,000
Development	1,412,000									1,412,000
Estimated Total Cumulative Development Costs										7,000,000	[3]
Completion date (or anticipated completion date, if under construction)										08/14
World Houston 40 [Member] | Under construction [Member]
Real Estate [Abstract]
Development	2,030,000									2,030,000
DEVELOPMENT [Abstract]
Size (Unaudited) (Square feet)	202,000									202,000
Development Costs Transferred										1,354,000	[2]
Development costs incurred, for the period										676,000
Development	2,030,000									2,030,000
Estimated Total Cumulative Development Costs										11,700,000	[3]
Completion date (or anticipated completion date, if under construction)										09/14
Tampa West Distribution Center V [Member]
Real Estate Property Sales [Abstract]
Date of property sale										12/20/2013
Net Sales Price										609,000
Basis										442,000
Recognized Gain										167,000
Size (in square feet) of property sold										12,000
Tampa West Distribution Center VII [Member]
Real Estate Property Sales [Abstract]
Date of property sale										12/20/2013
Net Sales Price										422,000
Basis										417,000
Recognized Gain										5,000
Size (in square feet) of property sold										6,000
Tampa East Distribution Center II [Member]
Real Estate Property Sales [Abstract]
Date of property sale										12/30/2013
Net Sales Price										1,929,000
Basis										1,303,000
Recognized Gain										626,000
Size (in square feet) of property sold										31,000
Tampa East Distribution Center III and Tampa West Distribution Center VIII [Member]
Real Estate Property Sales [Abstract]
Date of property sale												2/15/2012
Net Sales Price												538,000
Basis												371,000
Recognized Gain												167,000
Size (in square feet) of property sold												10,500
Estrella Distribution Center [Member]
Real Estate Property Sales [Abstract]
Date of property sale												6/13/2012
Net Sales Price												6,861,000
Basis												4,992,000
Recognized Gain												1,869,000
Size (in square feet) of property sold												174,000
Braniff Distribution Center [Member]
Real Estate Property Sales [Abstract]
Date of property sale												12/27/12
Net Sales Price												9,688,000
Basis												5,214,000
Recognized Gain												$ 4,474,000
Size (in square feet) of property sold												259,000

[1] 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 $19.8 million and tenant improvement obligations of $6.6 million on properties under development.

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