Segments - Net Income of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information
Rental revenues	$ 27,096	$ 25,305	$ 81,083	$ 72,839
Rental expenses	6,830	5,834	19,069	16,234
Real estate taxes	2,693	2,356	7,797	7,087
Segment revenues	41,201	38,552	161,391	108,555
Segment expenses	39,377	37,274	154,588	104,336
Net operating income	7,980	6,858	24,713	19,567
Operating Segments
Segment Reporting Information
Net operating income	19,397	18,393	61,020	53,737
Operating Segments | Office real estate
Segment Reporting Information
Rental revenues	4,762	5,277	14,427	16,097
Rental expenses	1,447	1,553	4,138	4,307
Real estate taxes	481	485	1,381	1,550
Net operating income	2,834	3,239	8,908	10,240
Operating Segments | Retail real estate
Segment Reporting Information
Rental revenues	15,880	14,340	47,089	41,485
Rental expenses	2,699	2,264	7,698	6,820
Real estate taxes	1,588	1,339	4,557	3,953
Net operating income	11,593	10,737	34,834	30,712
Operating Segments | Multifamily residential real estate
Segment Reporting Information
Rental revenues	6,454	5,688	19,567	15,257
Rental expenses	2,684	2,017	7,233	5,107
Real estate taxes	624	532	1,859	1,584
Net operating income	3,146	3,139	10,475	8,566
Operating Segments | General contracting and real estate services
Segment Reporting Information
Segment revenues	41,201	38,552	161,391	108,555
Segment expenses	39,377	37,274	154,588	104,336
Net operating income	$ 1,824	$ 1,278	$ 6,803	$ 4,219