Investment in Unconsolidated Joint Ventures (Summary of Operations) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Schedule of Equity Method Investments [Line Items]
Total Revenues	$ 71,194	$ 86,089
Net Income (Loss)	14,079	74,123
Company's Share of Income (Loss)	10,173	43,362
Charlotte Gateway Village, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	20,043	20,125
Net Income (Loss)	7,792	7,202
Company's Share of Income (Loss)	3,896	3,601
Wildwood Associates
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	0
Net Income (Loss)	(1,108)	(86)
Company's Share of Income (Loss)	2,739	(43)
Terminus Office Holdings
Schedule of Equity Method Investments [Line Items]
Total Revenues	33,545	33,503
Net Income (Loss)	4,424	4,907
Company's Share of Income (Loss)	2,276	2,453
Crawford Long - CPI, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	9,381	9,017
Net Income (Loss)	2,631	2,285
Company's Share of Income (Loss)	1,254	1,142
HICO Victory Center LP
Schedule of Equity Method Investments [Line Items]
Total Revenues	282	320
Net Income (Loss)	282	320
Company's Share of Income (Loss)	160	171
Austin 300 Colorado Project, LP
Schedule of Equity Method Investments [Line Items]
Total Revenues	385	0
Net Income (Loss)	173	0
Company's Share of Income (Loss)	86	0
Temco Associates, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	128	144
Net Income (Loss)	58	70
Company's Share of Income (Loss)	32	35
Courvoisier Centre JV, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	12,701
Net Income (Loss)	0	(1,000)
Company's Share of Income (Loss)	5	(80)
111 West Rio Building
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	0
Net Income (Loss)	0	0
Company's Share of Income (Loss)	0	(2,592)
AMCO 120 WT Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	0
Net Income (Loss)	(28)	(22)
Company's Share of Income (Loss)	0	0
DC Charlotte Plaza LLLP
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	2
Net Income (Loss)	0	2
Company's Share of Income (Loss)	(1)	1
EP I LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	27	4,094
Net Income (Loss)	1	44,865
Company's Share of Income (Loss)	(5)	28,479
HICO Avalon II, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	0
Net Income (Loss)	(14)	0
Company's Share of Income (Loss)	(10)	0
EP II LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	2,644
Net Income (Loss)	(21)	13,023
Company's Share of Income (Loss)	(15)	9,768
CL Realty, L.L.C.
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	2,899
Net Income (Loss)	(116)	2,657
Company's Share of Income (Loss)	(71)	408
Carolina Square Holdings LP
Schedule of Equity Method Investments [Line Items]
Total Revenues	7,403	640
Net Income (Loss)	5	(100)
Company's Share of Income (Loss)	$ (173)	$ 19