Segments - Net Income of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information
Rental revenues	$ 26,755	$ 24,251	$ 53,987	$ 47,534
Rental expenses	6,171	5,071	12,239	10,400
Real estate taxes	2,595	2,382	5,104	4,731
Segment revenues	56,671	33,200	120,190	70,003
Segment expenses	54,015	32,025	115,211	67,062
Net operating income	8,267	6,710	16,733	12,709
Operating Segments
Segment Reporting Information
Net operating income	20,645	17,973	41,623	35,344
Office real estate | Operating Segments
Segment Reporting Information
Rental revenues	4,759	5,299	9,665	10,820
Rental expenses	1,366	1,298	2,692	2,754
Real estate taxes	450	526	900	1,065
Net operating income	2,943	3,475	6,073	7,001
Retail real estate | Operating Segments
Segment Reporting Information
Rental revenues	15,578	14,113	31,209	27,145
Rental expenses	2,479	2,220	4,999	4,556
Real estate taxes	1,520	1,330	2,969	2,614
Net operating income	11,579	10,563	23,241	19,975
Multifamily residential real estate | Operating Segments
Segment Reporting Information
Rental revenues	6,418	4,839	13,113	9,569
Rental expenses	2,326	1,553	4,548	3,090
Real estate taxes	625	526	1,235	1,052
Net operating income	3,467	2,760	7,330	5,427
General contracting and real estate services | Operating Segments
Segment Reporting Information
Segment revenues	56,671	33,200	120,190	70,003
Segment expenses	54,015	32,025	115,211	67,062
Net operating income	$ 2,656	$ 1,175	$ 4,979	$ 2,941