Investment in Unconsolidated Joint Ventures (Summary of Financial Data and Principal Activities) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
SUMMARY OF FINANCIAL POSITION:
Total Assets	$ 930,904	$ 644,880
Total Debt	526,458	401,977
Total Equity (Deficit)	366,113	219,079
Company's Investment	156,388	79,434
SUMMARY OF OPERATIONS:
Total Revenues	116,855	110,689	$ 109,326
Net Income (Loss)	27,398	23,711	25,357
Company's Share of Net Income (Loss)	10,562	8,302	11,268
Terminus Office Holdings
SUMMARY OF FINANCIAL POSITION:
Total Assets	268,242	277,444
Total Debt	207,545	211,216
Total Equity (Deficit)	49,476	56,369
Company's Investment	25,686	29,110
SUMMARY OF OPERATIONS:
Total Revenues	42,386	40,250	39,531
Net Income (Loss)	4,608	2,789	663
Company's Share of Net Income (Loss)	2,303	1,395	308
EP I LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	78,537	83,115
Total Debt	58,029	58,029
Total Equity (Deficit)	18,962	24,172
Company's Investment	18,551	21,502
SUMMARY OF OPERATIONS:
Total Revenues	12,239	12,558	12,049
Net Income (Loss)	2,294	3,177	2,583
Company's Share of Net Income (Loss)	1,684	2,197	1,937
EP II LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	67,754	70,704
Total Debt	44,969	40,910
Total Equity (Deficit)	21,743	24,331
Company's Investment	17,606	19,118
SUMMARY OF OPERATIONS:
Total Revenues	5,376	1,264	0
Net Income (Loss)	(1,187)	(638)	0
Company's Share of Net Income (Loss)	(878)	(466)	0
Charlotte Gateway Village, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	119,054	123,531
Total Debt	0	17,536
Total Equity (Deficit)	116,809	104,336
Company's Investment	11,796	11,190
SUMMARY OF OPERATIONS:
Total Revenues	34,156	33,724	33,903
Net Income (Loss)	14,536	12,737	11,645
Company's Share of Net Income (Loss)	2,194	1,183	1,176
HICO Victory Center LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	14,124	13,532
Total Debt	0	0
Total Equity (Deficit)	13,869	13,229
Company's Investment	9,506	9,138
SUMMARY OF OPERATIONS:
Total Revenues	383	262	0
Net Income (Loss)	376	204	0
Company's Share of Net Income (Loss)	187	102	0
Carolina Square Holdings LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	66,922	15,729
Total Debt	23,741	0
Total Equity (Deficit)	34,173	12,085
Company's Investment	18,325	6,782
SUMMARY OF OPERATIONS:
Total Revenues	58	0	0
Net Income (Loss)	9	0	0
Company's Share of Net Income (Loss)	0	0	0
CL Realty, L.L.C.
SUMMARY OF FINANCIAL POSITION:
Total Assets	8,047	7,872
Total Debt	0	0
Total Equity (Deficit)	7,899	7,662
Company's Investment	3,644	3,515
SUMMARY OF OPERATIONS:
Total Revenues	567	855	1,573
Net Income (Loss)	237	424	1,069
Company's Share of Net Income (Loss)	128	220	542
DC Charlotte Plaza LLLP
SUMMARY OF FINANCIAL POSITION:
Total Assets	17,940	0
Total Debt	0	0
Total Equity (Deficit)	17,073	0
Company's Investment	8,937	0
SUMMARY OF OPERATIONS:
Total Revenues	47	0	0
Net Income (Loss)	45	0	0
Company's Share of Net Income (Loss)	24	0	0
Temco Associates, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	4,368	5,284
Total Debt	0	0
Total Equity (Deficit)	4,253	5,133
Company's Investment	829	977
SUMMARY OF OPERATIONS:
Total Revenues	1,343	9,485	2,155
Net Income (Loss)	440	2,358	495
Company's Share of Net Income (Loss)	502	2,351	(6)
Wildwood Associates
SUMMARY OF FINANCIAL POSITION:
Total Assets	16,351	16,419
Total Debt	0	0
Total Equity (Deficit)	16,314	16,354
Company's Investment	(1,143)	(1,122)
SUMMARY OF OPERATIONS:
Total Revenues	0	0	3,329
Net Income (Loss)	(140)	(120)	(1,704)
Company's Share of Net Income (Loss)	(70)	(59)	2,097
Crawford Long - CPI, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	27,523	29,143
Total Debt	72,822	74,286
Total Equity (Deficit)	(45,928)	(46,238)
Company's Investment	(21,866)	(22,021)
SUMMARY OF OPERATIONS:
Total Revenues	12,113	12,291	11,945
Net Income (Loss)	2,743	2,820	2,775
Company's Share of Net Income (Loss)	1,372	1,416	1,407
Cousins W. Rio Salado, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	59,399	0
Total Debt	12,852	0
Total Equity (Deficit)	32,855	0
Company's Investment	52,206	0
SUMMARY OF OPERATIONS:
Total Revenues	4,219	0	0
Net Income (Loss)	3,926	0	0
Company's Share of Net Income (Loss)	2,906	0	0
Courvoisier Centre JV, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	172,197	0
Total Debt	106,500	0
Total Equity (Deficit)	69,479	0
Company's Investment	11,782	0
AMCO 120 WT Holdings, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	10,446	0
Total Debt	0	0
Total Equity (Deficit)	9,136	0
Company's Investment	184	0
Courvoisier Centre JV, LLC
SUMMARY OF OPERATIONS:
Total Revenues	3,968	0	0
Net Income (Loss)	(489)	0	0
Company's Share of Net Income (Loss)	(93)	0	0
Other
SUMMARY OF FINANCIAL POSITION:
Total Assets	0	2,107
Total Debt	0	0
Total Equity (Deficit)	0	1,646
Company's Investment	345	1,245
SUMMARY OF OPERATIONS:
Total Revenues	0	0	4,841
Net Income (Loss)	0	(40)	7,831
Company's Share of Net Income (Loss)	$ 303	$ (37)	$ 3,807