Segments - Rental Revenues of Reportable Segments (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Rental revenues	$ 15,319,000	$ 14,231,000	$ 30,512,000	$ 27,629,000
Office Real Estate [Member]
Segment Reporting Information [Line Items]
Minimum rents	6,220,000	6,105,000	12,372,000	12,205,000
Percentage rents			45,000	104,000
Other	299,000	315,000	651,000	597,000
Rental revenues	6,519,000	6,420,000	13,068,000	12,906,000
Retail Real Estate [Member]
Segment Reporting Information [Line Items]
Minimum rents	4,819,000	4,609,000	9,593,000	8,974,000
Percentage rents	46,000	29,000	137,000	53,000
Other	838,000	745,000	1,743,000	1,361,000
Rental revenues	5,703,000	5,383,000	11,473,000	10,388,000
Multifamily Residential Real Estate [Member]
Segment Reporting Information [Line Items]
Minimum rents	2,643,000	2,063,000	5,093,000	3,690,000
Percentage rents	24,000	21,000	59,000	63,000
Other	430,000	344,000	819,000	582,000
Rental revenues	$ 3,097,000	$ 2,428,000	$ 5,971,000	$ 4,335,000