Investment in Unconsolidated Joint Ventures (Summary of Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SUMMARY OF OPERATIONS
Total Revenues	$ 95,515	$ 110,664	$ 116,855
Net Income (Loss)	15,352	77,944	27,398
Company's Share of Net Income (Loss)	12,224	47,115	10,562
Charlotte Gateway Village, LLC
SUMMARY OF OPERATIONS
Total Revenues	26,932	26,465	34,156
Net Income (Loss)	10,285	9,528	14,536
Company's Share of Net Income (Loss)	5,143	4,764	2,194
Terminus Office Holdings
SUMMARY OF OPERATIONS
Total Revenues	44,429	43,959	42,386
Net Income (Loss)	5,506	6,307	4,608
Company's Share of Net Income (Loss)	2,755	3,153	2,303
Wildwood Associates
SUMMARY OF OPERATIONS
Total Revenues	0	0	0
Net Income (Loss)	(1,140)	(116)	(140)
Company's Share of Net Income (Loss)	2,723	(58)	(70)
Crawford Long - CPI, LLC
SUMMARY OF OPERATIONS
Total Revenues	12,383	12,079	12,113
Net Income (Loss)	3,446	3,171	2,743
Company's Share of Net Income (Loss)	1,641	1,572	1,372
HICO Victory Center LP
SUMMARY OF OPERATIONS
Total Revenues	400	429	383
Net Income (Loss)	400	431	376
Company's Share of Net Income (Loss)	219	225	187
Austin 300 Colorado Project, LP
SUMMARY OF OPERATIONS
Total Revenues	487	0	0
Net Income (Loss)	220	0	0
Company's Share of Net Income (Loss)	110	0	0
Temco Associates, LLC
SUMMARY OF OPERATIONS
Total Revenues	176	192	1,343
Net Income (Loss)	(2,965)	123	440
Company's Share of Net Income (Loss)	43	46	502
Courvoisier Centre JV, LLC
SUMMARY OF OPERATIONS
Total Revenues	0	15,106	3,968
Net Income (Loss)	0	(1,750)	(489)
Company's Share of Net Income (Loss)	5	521	(93)
DC Charlotte Plaza LLLP
SUMMARY OF OPERATIONS
Total Revenues	0	2	47
Net Income (Loss)	0	2	45
Company's Share of Net Income (Loss)	(1)	1	24
EP II LLC
SUMMARY OF OPERATIONS
Total Revenues	5	2,644	5,376
Net Income (Loss)	(16)	13,008	(1,187)
Company's Share of Net Income (Loss)	(14)	9,756	(878)
EP I LLC
SUMMARY OF OPERATIONS
Total Revenues	17	4,123	12,239
Net Income (Loss)	(23)	45,115	2,294
Company's Share of Net Income (Loss)	(20)	28,667	1,684
CL Realty, L.L.C.
SUMMARY OF OPERATIONS
Total Revenues	0	2,964	567
Net Income (Loss)	(161)	2,668	237
Company's Share of Net Income (Loss)	(94)	536	128
Carolina Square Holdings LP
SUMMARY OF OPERATIONS
Total Revenues	10,686	2,701	58
Net Income (Loss)	(169)	(532)	9
Company's Share of Net Income (Loss)	(275)	522	0
AMCO 120 WT Holdings, LLC
SUMMARY OF OPERATIONS
Total Revenues	0	0	0
Net Income (Loss)	38	58	0
Company's Share of Net Income (Loss)	0	0	0
Other
SUMMARY OF OPERATIONS
Total Revenues	0	0	4,219
Net Income (Loss)	(69)	(69)	3,926
Company's Share of Net Income (Loss)	$ (11)	$ (2,590)	$ 3,209