Derivative Instruments - Schedule of Interest Rate Swap Derivative Instruments (Detail) (USD $)	9 Months Ended		12 Months Ended
	Sep. 30, 2012		Dec. 31, 2011
Non-qualifying Interest Rate Swap on Thames Valley Drive Retail Park debt [Member]
Derivative [Line Items]
Notional Amount	$ 9,107,000	[1]	$ 8,762,000	[1]
Fair Value	(288,000)	[1]	(520,000)	[1]
Pay Fixed Rate	5.41%	[1]	5.41%	[1]
Receive Variable Rate	0.68%	[1]	1.04%	[1]
Maturity Date	May 30, 2013	[1]	May 30, 2013	[1]
Non-qualifying Interest Rate Swap on Albion Mills debt [Member]
Derivative [Line Items]
Notional Amount	9,227,000	[1]	8,877,000	[1]
Fair Value	(317,000)	[1]	(438,000)	[1]
Pay Fixed Rate	3.94%	[1]	3.94%	[1]
Receive Variable Rate	0.86%	[1]	0.96%	[1]
Maturity Date	Oct. 10, 2013	[1]	Oct. 10, 2013	[1]
Qualifying Interest Rate Swap on Maskew Retail Park debt [Member]
Derivative [Line Items]
Notional Amount	22,566,000	[1]	21,710,000	[1]
Fair Value	(1,170,000)	[1]	(1,250,000)	[1]
Pay Fixed Rate	3.42%	[1]	3.42%	[1]
Receive Variable Rate	0.78%	[1]	0.97%	[1]
Maturity Date	Aug. 10, 2014	[1]	Aug. 10, 2014	[1]
Qualifying Interest Rate Swap on Pacific Corporate Park Debt [Member]
Derivative [Line Items]
Notional Amount	79,750,000		82,000,000
Fair Value	(7,006,000)		(5,721,000)
Pay Fixed Rate	2.69%		2.69%
Receive Variable Rate	0.25%		0.32%
Maturity Date	Dec. 07, 2017		Dec. 07, 2017
Qualifying Interest Rate Swap on 100 Kimball Drive debt [Member]
Derivative [Line Items]
Notional Amount	32,023,000		32,521,000
Fair Value	(4,869,000)		(4,120,000)
Pay Fixed Rate	3.50%		3.50%
Receive Variable Rate	0.23%		0.27%
Maturity Date	Mar. 01, 2021		Mar. 01, 2021
Qualifying Interest Rate Swap on Kings Mountain III debt [Member]
Derivative [Line Items]
Notional Amount	11,401,000		11,595,000
Fair Value	(957,000)		(709,000)
Pay Fixed Rate	2.47%		2.47%
Receive Variable Rate	0.23%		0.27%
Maturity Date	Jul. 01, 2018		Jul. 01, 2018
Qualifying Interest Rate Swap on Wells Fargo Credit Facility loan [Member]
Derivative [Line Items]
Notional Amount			15,000,000
Fair Value			$ (540,000)
Pay Fixed Rate			2.10%
Receive Variable Rate			0.27%
Maturity Date			May 26, 2014

[1] Based on three month GBP-based LIBOR BBA Index with variable rate reset dates every 90 days during the term of the swaps.