Investment in Unconsolidated Joint Ventures (Summary of Financial Position and Operations) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
SUMMARY OF FINANCIAL POSITION:
Total Assets	$ 867,201		$ 779,204
Total Debt	340,429		342,892
Total Equity	379,541		338,427
Company’s Investment	155,469		140,376
SUMMARY OF OPERATIONS:
Total Revenues	56,338	$ 48,001
Net Income (Loss)	13,256	9,624
Company's Share of Income (Loss)	6,538	7,921
Terminus Office Holdings LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	261,023		258,060
Total Debt	196,451		198,732
Total Equity	54,358		50,539
Company’s Investment	50,183		48,571
SUMMARY OF OPERATIONS:
Total Revenues	24,050	22,318
Net Income (Loss)	3,819	3,070
Company's Share of Income (Loss)	1,800	1,597
DC Charlotte Plaza LLLP
SUMMARY OF FINANCIAL POSITION:
Total Assets	179,802		155,530
Total Debt	0		0
Total Equity	91,780		88,922
Company’s Investment	48,660		46,554
SUMMARY OF OPERATIONS:
Total Revenues	5,410	0
Net Income (Loss)	2,201	0
Company's Share of Income (Loss)	1,101	0
Austin 300 Colorado Project, LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	76,136		51,180
Total Debt	1		0
Total Equity	54,951		41,298
Company’s Investment	29,576		22,335
SUMMARY OF OPERATIONS:
Total Revenues	222	285
Net Income (Loss)	110	172
Company's Share of Income (Loss)	55	86
Carolina Square Holdings LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	115,324		106,187
Total Debt	75,234		74,638
Total Equity	27,005		28,844
Company’s Investment	15,915		16,840
SUMMARY OF OPERATIONS:
Total Revenues	6,491	5,361
Net Income (Loss)	158	445
Company's Share of Income (Loss)	110	17
HICO Victory Center LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	15,220		15,069
Total Debt	0		0
Total Equity	15,076		14,801
Company’s Investment	10,176		10,003
SUMMARY OF OPERATIONS:
Total Revenues	235	202
Net Income (Loss)	235	202
Company's Share of Income (Loss)	137	106
Charlotte Gateway Village, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	112,792		112,553
Total Debt	0		0
Total Equity	108,714		109,666
Company’s Investment	7,749		8,225
SUMMARY OF OPERATIONS:
Total Revenues	13,611	13,477
Net Income (Loss)	5,049	5,189
Company's Share of Income (Loss)	2,524	2,594
AMCO 120 WT Holdings, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	58,557		36,680
Total Debt	0		0
Total Equity	51,567		31,372
Company’s Investment	9,747		5,538
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	(32)	(24)
Company's Share of Income (Loss)	0	0
CL Realty, L.L.C.
SUMMARY OF FINANCIAL POSITION:
Total Assets	4,166		4,169
Total Debt	0		0
Total Equity	4,093		4,183
Company’s Investment	2,842		2,886
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	(75)	(71)
Company's Share of Income (Loss)	(44)	(49)
Temco Associates, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	1,526		1,482
Total Debt	0		0
Total Equity	1,423		1,379
Company’s Investment	941		919
SUMMARY OF OPERATIONS:
Total Revenues	64	80
Net Income (Loss)	36	36
Company's Share of Income (Loss)	22	21
TR 208 Nueces Member, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	2,692		0
Total Debt	0		0
Total Equity	1,396		0
Company’s Investment	349		0
EP II LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	246		247
Total Debt	0		0
Total Equity	164		165
Company’s Investment	29		30
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	(1)	(21)
Company's Share of Income (Loss)	(1)	(15)
EP I LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	458		461
Total Debt	0		0
Total Equity	293		296
Company’s Investment	2		6
SUMMARY OF OPERATIONS:
Total Revenues	0	19
Net Income (Loss)	(3)	(4)
Company's Share of Income (Loss)	(4)	(5)
Wildwood Associates
SUMMARY OF FINANCIAL POSITION:
Total Assets	11,138		11,157
Total Debt	0		0
Total Equity	11,058		11,108
Company’s Investment	(492)		(460)
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	(50)	(1,086)
Company's Share of Income (Loss)	(25)	2,750
Crawford Long - CPI, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	28,121		26,429
Total Debt	68,743		69,522
Total Equity	(42,337)		(44,146)
Company’s Investment	(20,208)		$ (21,071)
SUMMARY OF OPERATIONS:
Total Revenues	6,255	6,259
Net Income (Loss)	1,809	1,730
Company's Share of Income (Loss)	863	824
Other
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	0	(14)
Company's Share of Income (Loss)	$ 0	$ (5)