Investment in Unconsolidated Joint Ventures (Summary of Operations) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Schedule of Equity Method Investments [Line Items]
Total Revenues	$ 48,001	$ 57,513
Net Income (Loss)	9,624	68,713
Company's Share of Income (Loss)	7,921	40,901
Wildwood Associates
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	0
Net Income (Loss)	(1,086)	(51)
Company's Share of Income (Loss)	2,750	(26)
Charlotte Gateway Village, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	13,477	13,380
Net Income (Loss)	5,189	4,734
Company's Share of Income (Loss)	2,594	2,367
Terminus Office Holdings
Schedule of Equity Method Investments [Line Items]
Total Revenues	22,318	21,908
Net Income (Loss)	3,070	3,178
Company's Share of Income (Loss)	1,597	1,769
Crawford Long - CPI, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	6,259	6,033
Net Income (Loss)	1,730	1,516
Company's Share of Income (Loss)	824	758
HICO Victory Center LP
Schedule of Equity Method Investments [Line Items]
Total Revenues	202	171
Net Income (Loss)	202	171
Company's Share of Income (Loss)	106	114
Austin 300 Colorado Project, LP
Schedule of Equity Method Investments [Line Items]
Total Revenues	285	0
Net Income (Loss)	172	0
Company's Share of Income (Loss)	86	0
Temco Associates, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	80	80
Net Income (Loss)	36	41
Company's Share of Income (Loss)	21	25
Carolina Square Holdings LP
Schedule of Equity Method Investments [Line Items]
Total Revenues	5,361	40
Net Income (Loss)	445	(94)
Company's Share of Income (Loss)	17	0
Courvoisier Centre JV, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	6,554
Net Income (Loss)	0	(1,083)
Company's Share of Income (Loss)	5	(195)
EP I LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	19	4,103
Net Income (Loss)	(4)	44,929
Company's Share of Income (Loss)	(5)	28,525
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	2,643
Net Income (Loss)	(21)	12,967
Company's Share of Income (Loss)	(15)	9,725
CL Realty, L.L.C.
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	2,599
Net Income (Loss)	(71)	2,415
Company's Share of Income (Loss)	(49)	430
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)	0	2
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	(2,593)
AMCO 120 WT Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	0
Net Income (Loss)	(24)	(12)
Company's Share of Income (Loss)	$ 0	$ 0