SCHEDULE III SCHEDULE III (Details2) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance at beginning of year	$ 1,662,593,000	[1]	$ 1,521,177,000	[1]	$ 1,468,182,000
Purchase of real estate properties	48,934,000		80,624,000		19,897,000
Development of real estate properties	55,404,000		42,148,000		9,145,000
Improvements to real estate properties	18,164,000		18,686,000		23,953,000
Carrying amount of investments sold	(16,756,000)		0		0
Write-off of improvements	(307,000)		(42,000)		0
Balance at end of year	1,768,032,000	[1]	1,662,593,000	[1]	1,521,177,000	[1]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance at beginning of year	451,805,000		403,187,000		354,745,000
Depreciation expense	51,564,000		48,648,000		48,442,000
Accumulated depreciation on assets sold	(6,819,000)		0		0
Other	(303,000)		(30,000)		0
Balance at end of year	496,247,000		451,805,000		403,187,000
Estimated aggregate cost of real estate properties for federal income tax purposes	1,727,509,000
Estimated accumulated tax depreciation	314,360,000
Percentage of Occupation When Development Cost Ceased Being Capitalized	80.00%
Length of Time After Project Completion When Development Cost Ceased Being Capitalized	1 year
Loan Amount	607,766,000		628,170,000
Recourse liability	5,000,000
Castilian Research Center [Member]
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Noncontrolling Interests (in hundreths)	20.00%
Noncontrolling Interests	1,794,000		1,794,000
University Business Center [Member]
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Noncontrolling Interests (in hundreths)	20.00%
Noncontrolling Interests	6,418,000		6,369,000
Buildings [Member]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Estimated useful life (in years)	40 years
Minimum [Member] | Improvements and Personal Property [Member]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Estimated useful life (in years)	3 years
Maximum [Member] | Improvements and Personal Property [Member]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Estimated useful life (in years)	15 years
Dominguez, Industry I and III, Kingsview, Shaw, Walnut and Washington [Member]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	61,052,000	[2]	62,875,000	[2]
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]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	60,310,000		63,093,000
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]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	61,970,000		64,014,000
Arion 18, Beltway VI & VII, Commerce Park II & III, Concord Dist Ctr, Interstate Dist Ctr V, VI & VII, Lakeview Business Ctr, Ridge Creek Distribution Ctr II, Southridge IV & V and World Houston 32 [Member]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	52,369,000		0
Thirty Fifth Avenue, Beltway I, Broadway V, Lockwood, Northwest Point, Sunbelt, Techway Southwest I and World Houston 10, 11 and 14 [Member]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	34,474,000		35,912,000
Americas Ten I, Kirby, Palm River North I, II and III, Shady Trail, Westlake I and II and World Houston 17 [Member]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	27,467,000		27,996,000
Country Club I, Lake Pointe, Techway Southwest II and World Houston 19 and 20 [Member]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	29,465,000		31,039,000
Huntwood and Wiegman Distribution Centers [Member]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	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]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	63,132,000		65,961,000
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]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	64,374,000		67,188,000
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]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	52,086,000		54,001,000
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]
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Loan Amount	$ 69,376,000		$ 71,837,000

[1] Includes 20% noncontrolling interests in Castilian Research Center of $1,794,000 at December 31, 2012 and $1,794,000 at December 31, 2011 and in University Business Center of $6,418,000 and $6,369,000, respectively.

[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.