Investment in Unconsolidated Joint Ventures (Summary of Financial Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
SUMMARY OF FINANCIAL POSITION
Total Assets	$ 779,204	$ 643,134
Total Debt	342,892	338,590
Total Equity (Deficit)	338,427	267,423
Company's Investment	140,376	78,940
Terminus Office Holdings
SUMMARY OF FINANCIAL POSITION
Total Assets	258,060	261,999
Total Debt	198,732	203,131
Total Equity (Deficit)	50,539	48,033
Company's Investment	48,571	24,898
DC Charlotte Plaza LLLP
SUMMARY OF FINANCIAL POSITION
Total Assets	155,530	53,791
Total Debt	0	0
Total Equity (Deficit)	88,922	42,853
Company's Investment	46,554	22,293
Austin 300 Colorado Project, LP
SUMMARY OF FINANCIAL POSITION
Total Assets	51,180	0
Total Debt	0	0
Total Equity (Deficit)	41,298	0
Company's Investment	22,335	0
Carolina Square Holdings LP
SUMMARY OF FINANCIAL POSITION
Total Assets	106,187	106,580
Total Debt	74,638	64,412
Total Equity (Deficit)	28,844	33,648
Company's Investment	16,840	19,384
HICO Victory Center LP
SUMMARY OF FINANCIAL POSITION
Total Assets	15,069	14,403
Total Debt	0	0
Total Equity (Deficit)	14,801	14,401
Company's Investment	10,003	9,752
Charlotte Gateway Village, LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	112,553	124,691
Total Debt	0	0
Total Equity (Deficit)	109,666	121,386
Company's Investment	8,225	14,568
AMCO 120 WT Holdings, LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	36,680	18,066
Total Debt	0	0
Total Equity (Deficit)	31,372	16,354
Company's Investment	5,538	1,664
CL Realty, L.L.C.
SUMMARY OF FINANCIAL POSITION
Total Assets	4,169	8,287
Total Debt	0	0
Total Equity (Deficit)	4,183	8,127
Company's Investment	2,886	2,980
Temco Associates, LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	1,482	4,441
Total Debt	0	0
Total Equity (Deficit)	1,379	4,337
Company's Investment	919	875
EP II LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	247	277
Total Debt	0	0
Total Equity (Deficit)	165	180
Company's Investment	30	44
EP I LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	461	521
Total Debt	0	0
Total Equity (Deficit)	296	319
Company's Investment	6	25
Wildwood Associates
SUMMARY OF FINANCIAL POSITION
Total Assets	11,157	16,337
Total Debt	0	0
Total Equity (Deficit)	11,108	16,297
Company's Investment	(460)	(1,151)
Crawford Long - CPI, LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	26,429	27,362
Total Debt	69,522	71,047
Total Equity (Deficit)	(44,146)	(44,815)
Company's Investment	(21,071)	(21,323)
Other
SUMMARY OF FINANCIAL POSITION
Total Assets	0	6,379
Total Debt	0	0
Total Equity (Deficit)	0	6,303
Company's Investment	$ 0	$ 4,931