Segments - Rental Revenues of Reportable Segments (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]
Rental revenues	$ 16,713,000	$ 14,899,000	$ 47,225,000	$ 42,528,000
Office Real Estate [Member]
Segment Reporting Information [Line Items]
Minimum rents	6,954,000	6,059,000	19,326,000	18,264,000
Percentage rents			45,000	104,000
Other	341,000	304,000	992,000	901,000
Rental revenues	7,295,000	6,364,000	20,363,000	19,270,000
Retail Real Estate [Member]
Segment Reporting Information [Line Items]
Minimum rents	5,167,000	4,759,000	14,760,000	13,733,000
Percentage rents	36,000	35,000	173,000	88,000
Other	883,000	890,000	2,626,000	2,251,000
Rental revenues	6,086,000	5,683,000	17,559,000	16,071,000
Multifamily Residential Real Estate [Member]
Segment Reporting Information [Line Items]
Minimum rents	2,813,000	2,370,000	7,906,000	6,060,000
Percentage rents	19,000	21,000	78,000	84,000
Other	500,000	461,000	1,319,000	1,043,000
Rental revenues	$ 3,332,000	$ 2,852,000	$ 9,303,000	$ 7,187,000