Segment Information (Textual) (Details)		6 Months Ended
	Feb. 02, 2017 property	Jun. 30, 2017 property segment
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment		5
Office Properties [Member]
Segment Reporting Information [Line Items]
Number of Properties Sold		12
Office Properties [Member] | 1200 & 1220 Concord Avenue (Concord Airport Plaza) [Member]
Segment Reporting Information [Line Items]
Number of Properties Sold	2	2