Segments - Rental Revenues of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information
Rental revenues	$ 21,771	$ 21,303	$ 19,908	$ 18,190	$ 17,521	$ 16,713	$ 15,319	$ 15,193	$ 81,172	$ 64,746	$ 57,520
Straight-line rent revenue									1,924	2,203	1,055
Amortization of leasing incentive									(800)	(700)	(800)
Office Real Estate
Segment Reporting Information
Rental revenues									31,534	27,827	25,794
Retail Real Estate
Segment Reporting Information
Rental revenues									32,064	23,956	21,755
Multifamily Residential Real Estate
Segment Reporting Information
Rental revenues									$ 17,574	$ 12,963	$ 9,971