Investment in Unconsolidated Joint Ventures (Summary of Operations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
SUMMARY OF OPERATIONS
Total Revenues	$ 110,664	$ 116,855	$ 110,689
Net Income (Loss)	77,944	27,398	23,711
Company's Share of Net Income (Loss)	47,115	10,562	8,302
EP I LLC
SUMMARY OF OPERATIONS
Total Revenues	4,123	12,239	12,558
Net Income (Loss)	45,115	2,294	3,177
Company's Share of Net Income (Loss)	28,667	1,684	2,197
EP II LLC
SUMMARY OF OPERATIONS
Total Revenues	2,644	5,376	1,264
Net Income (Loss)	13,008	(1,187)	(638)
Company's Share of Net Income (Loss)	9,756	(878)	(466)
Charlotte Gateway Village, LLC
SUMMARY OF OPERATIONS
Total Revenues	26,465	34,156	33,724
Net Income (Loss)	9,528	14,536	12,737
Company's Share of Net Income (Loss)	4,764	2,194	1,183
Terminus Office Holdings
SUMMARY OF OPERATIONS
Total Revenues	43,959	42,386	40,250
Net Income (Loss)	6,307	4,608	2,789
Company's Share of Net Income (Loss)	3,153	2,303	1,395
Crawford Long - CPI, LLC
SUMMARY OF OPERATIONS
Total Revenues	12,079	12,113	12,291
Net Income (Loss)	3,171	2,743	2,820
Company's Share of Net Income (Loss)	1,572	1,372	1,416
CL Realty, L.L.C.
SUMMARY OF OPERATIONS
Total Revenues	2,964	567	855
Net Income (Loss)	2,668	237	424
Company's Share of Net Income (Loss)	536	128	220
Courvoisier Centre JV, LLC
SUMMARY OF OPERATIONS
Total Revenues	15,106	3,968	0
Net Income (Loss)	(1,750)	(489)	0
Company's Share of Net Income (Loss)	521	(93)	0
Carolina Square Holdings LP
SUMMARY OF OPERATIONS
Total Revenues	2,701	58	0
Net Income (Loss)	(532)	9	0
Company's Share of Net Income (Loss)	522	0	0
HICO Victory Center LP
SUMMARY OF OPERATIONS
Total Revenues	429	383	262
Net Income (Loss)	431	376	204
Company's Share of Net Income (Loss)	225	187	102
Temco Associates, LLC
SUMMARY OF OPERATIONS
Total Revenues	192	1,343	9,485
Net Income (Loss)	123	440	2,358
Company's Share of Net Income (Loss)	46	502	2,351
DC Charlotte Plaza LLLP
SUMMARY OF OPERATIONS
Total Revenues	2	47	0
Net Income (Loss)	2	45	0
Company's Share of Net Income (Loss)	1	24	0
HICO Avalon II, LLC
SUMMARY OF OPERATIONS
Total Revenues	0	0	0
Net Income (Loss)	(69)	0	0
Company's Share of Net Income (Loss)	0	0	0
AMCO 120 WT Holdings, LLC
SUMMARY OF OPERATIONS
Total Revenues	0	0	0
Net Income (Loss)	58	0	0
Company's Share of Net Income (Loss)	0	0	0
Wildwood Associates
SUMMARY OF OPERATIONS
Total Revenues	0	0	0
Net Income (Loss)	(116)	(140)	(120)
Company's Share of Net Income (Loss)	(58)	(70)	(59)
111 West Rio Building
SUMMARY OF OPERATIONS
Total Revenues	0	4,219	0
Net Income (Loss)	0	3,926	0
Company's Share of Net Income (Loss)	(2,590)	2,906	0
Other
SUMMARY OF OPERATIONS
Total Revenues	0	0	0
Net Income (Loss)	0	0	(40)
Company's Share of Net Income (Loss)	$ 0	$ 303	$ (37)