Variable Interest Entities - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Jan. 31, 2013
Variable Interest Entity [Line Items]
Number of identified consolidated variable interest entities		2
Identified investments	11	11
Investments with no equity at risk	7	7
Number of additional entities		4
Unconsolidated joint venture	11	11
Number of assets identified as variable interests in variable interest entities	4	4
Investments lacking the right to receive returns		1
1515 Market Street [Member]
Variable Interest Entity [Line Items]
Trust acquired equity			49.00%
Revenue	$ 2,449,000	$ 6,942,000
Net income	514,000	1,586,000
Cerritos [Member]
Variable Interest Entity [Line Items]
Land and building	22,079,000	22,079,000
Net of accumulated depreciation	830,000	830,000
Lease intangibles	3,435,000	3,435,000
Accumulated amortization	627,000	627,000
Cerritos [Member] | Mortgage Debt Notes A [Member]
Variable Interest Entity [Line Items]
Mortgage debt	23,153,000	23,153,000
Cerritos [Member] | Mortgage Debt Notes B [Member]
Variable Interest Entity [Line Items]
Mortgage debt	864,000	864,000
1515 Market Street Loan Modification [Member]
Variable Interest Entity [Line Items]
Land and building	42,950,000	42,950,000
Net of accumulated depreciation	590,000	590,000
Lease intangibles	16,624,000	16,624,000
Accumulated amortization	1,566,000	1,566,000
Trust acquired equity	49.00%	49.00%
1515 Market Street Loan Modification [Member] | First Mortgage [Member]
Variable Interest Entity [Line Items]
Mortgage debt	42,683,000	42,683,000
1515 Market Street Loan Modification [Member] | Original Mortgage [Member]
Variable Interest Entity [Line Items]
Mortgage debt	$ 35,040,000	$ 35,040,000