Segments - Net Income of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information
Rental revenues	$ 26,516	$ 25,305	$ 24,251	$ 23,283	$ 21,771	$ 21,303	$ 19,908	$ 18,190	$ 99,355	$ 81,172	$ 64,746
Rental expenses									21,904	19,204	16,667
Real estate taxes									9,629	7,782	5,743
Segment revenues	50,475	38,552	33,200	36,803	41,309	53,822	47,066	29,071	159,030	171,268	103,321
Segment expenses									153,375	165,344	98,754
Net operating income	$ 19,740	$ 18,393	$ 17,973	$ 17,371	$ 15,819	$ 16,488	$ 15,101	$ 12,702	26,679	26,584	21,379
Operating Segments
Segment Reporting Information
Net operating income									73,477	60,110	46,903
Operating Segments | Office real estate
Segment Reporting Information
Rental revenues									20,929	31,534	27,827
Rental expenses									5,560	6,938	6,395
Real estate taxes									2,000	2,950	2,315
Net operating income									13,369	21,646	19,117
Operating Segments | Retail real estate
Segment Reporting Information
Rental revenues									56,511	32,064	23,956
Rental expenses									9,116	5,915	5,011
Real estate taxes									5,395	2,928	2,097
Net operating income									42,000	23,221	16,848
Operating Segments | Multifamily residential real estate
Segment Reporting Information
Rental revenues									21,915	17,574	12,963
Rental expenses									7,228	6,351	5,261
Real estate taxes									2,234	1,904	1,331
Net operating income									12,453	9,319	6,371
Operating Segments | General contracting and real estate services
Segment Reporting Information
Segment revenues									159,030	171,268	103,321
Segment expenses									153,375	165,344	98,754
Net operating income									$ 5,655	$ 5,924	$ 4,567