Investment in Unconsolidated Joint Ventures (Summary of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Total Revenues	$ 23,732	$ 31,052
Net Income (Loss)	4,557	7,557
Company's Share of Income (Loss)	2,885	581
Charlotte Gateway Village, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	6,772	6,719
Net Income (Loss)	2,793	2,365
Company's Share of Income (Loss)	1,397	1,182
Terminus Office Holdings
Schedule of Equity Method Investments [Line Items]
Total Revenues	10,922	10,946
Net Income (Loss)	1,599	1,635
Company's Share of Income (Loss)	830	818
Crawford Long - CPI, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	3,126	3,019
Net Income (Loss)	823	769
Company's Share of Income (Loss)	391	384
Wildwood Associates
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	0
Net Income (Loss)	(1,000)	(29)
Company's Share of Income (Loss)	317	(14)
Courvoisier Centre JV, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	2,636
Net Income (Loss)	0	(388)
Company's Share of Income (Loss)	63	(96)
HICO Victory Center LP
Schedule of Equity Method Investments [Line Items]
Total Revenues	96	85
Net Income (Loss)	96	85
Company's Share of Income (Loss)	50	54
Austin 300 Colorado Project, LP
Schedule of Equity Method Investments [Line Items]
Total Revenues	150	0
Net Income (Loss)	99	0
Company's Share of Income (Loss)	49	0
Temco Associates, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	48	48
Net Income (Loss)	22	27
Company's Share of Income (Loss)	11	17
HICO Avalon II, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	0
Net Income (Loss)	(5)	0
Company's Share of Income (Loss)	(4)	0
EP II LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	1,910
Net Income (Loss)	(5)	137
Company's Share of Income (Loss)	(4)	99
EP I LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	4	3,065
Net Income (Loss)	(16)	544
Company's Share of Income (Loss)	(12)	282
CL Realty, L.L.C.
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	2,599
Net Income (Loss)	(44)	2,463
Company's Share of Income (Loss)	(28)	435
Carolina Square Holdings LP
Schedule of Equity Method Investments [Line Items]
Total Revenues	2,614	24
Net Income (Loss)	202	(45)
Company's Share of Income (Loss)	(175)	0
DC Charlotte Plaza LLLP
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	1
Net Income (Loss)	0	1
Company's Share of Income (Loss)	0	1
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	(2,581)
AMCO 120 WT Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Total Revenues	0	0
Net Income (Loss)	(7)	(7)
Company's Share of Income (Loss)	$ 0	$ 0