Investment in Unconsolidated Joint Ventures (Summary of Financial Position and Operations) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Feb. 29, 2020	Dec. 31, 2019
SUMMARY OF FINANCIAL POSITION:
Total Assets	$ 556,339			$ 658,303
Total Debt	185,843			165,039
Total Equity	243,567			354,404
Company’s Investment	110,208			114,158
SUMMARY OF OPERATIONS:
Total Revenues	19,455	$ 25,661
Net Income (Loss)	6,372	5,977
Company's Share of Income (Loss)	3,425	2,904
DC Charlotte Plaza LLLP
SUMMARY OF FINANCIAL POSITION:
Total Assets	179,082			179,694
Total Debt	0			0
Total Equity	92,162			90,373
Company’s Investment	48,807			48,058
SUMMARY OF OPERATIONS:
Total Revenues	5,276	410
Net Income (Loss)	1,789	410
Company's Share of Income (Loss)	750	205
Austin 300 Colorado Project, LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	140,520			112,630
Total Debt	42,226			21,430
Total Equity	68,145			68,101
Company’s Investment	37,239			36,846
SUMMARY OF OPERATIONS:
Total Revenues	98	126
Net Income (Loss)	44	72
Company's Share of Income (Loss)	22	36
AMCO 120 WT Holdings, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	79,703			77,377
Total Debt	0			0
Total Equity	74,908			70,696
Company’s Investment	14,146			13,362
SUMMARY OF OPERATIONS:
Total Revenues	138	0
Net Income (Loss)	(509)	(10)
Company's Share of Income (Loss)	(141)	0
Carolina Square Holdings LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	102,523			114,483
Total Debt	76,074			75,662
Total Equity	24,735			25,184
Company’s Investment	13,816			14,414
SUMMARY OF OPERATIONS:
Total Revenues	3,706	3,294
Net Income (Loss)	530	170
Company's Share of Income (Loss)	254	58
HICO Victory Center LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	15,543			16,045
Total Debt	0			0
Total Equity	15,479			15,353
Company’s Investment	10,460			10,373
SUMMARY OF OPERATIONS:
Total Revenues	126	130
Net Income (Loss)	126	130
Company's Share of Income (Loss)	63	62
Charlotte Gateway Village, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	0			109,675
Total Debt	0			0
Total Equity	0			106,651
Company’s Investment	0			6,718
SUMMARY OF OPERATIONS:
Total Revenues	6,572	6,743
Net Income (Loss)	3,296	2,524
Company's Share of Income (Loss)	1,647	1,262
Wildwood Associates
SUMMARY OF FINANCIAL POSITION:
Total Assets	0			11,061
Total Debt	0			0
Total Equity	0			10,978
Company’s Investment	0		$ (520)	(521)
Crawford Long - CPI, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	30,069			28,459
Total Debt	67,543			67,947
Total Equity	(39,215)			(40,250)
Company’s Investment	(18,708)			(19,205)
SUMMARY OF OPERATIONS:
Total Revenues	3,343	3,129
Net Income (Loss)	1,035	889
Company's Share of Income (Loss)	497	424
Terminus Office Holdings LLC
SUMMARY OF OPERATIONS:
Total Revenues	0	11,797
Net Income (Loss)	0	1,831
Company's Share of Income (Loss)	0	880
Other
SUMMARY OF FINANCIAL POSITION:
Total Assets	8,899			8,879
Total Debt	0			0
Total Equity	7,353			7,318
Company’s Investment	4,448			$ 4,113
SUMMARY OF OPERATIONS:
Total Revenues	196	32
Net Income (Loss)	61	(39)
Company's Share of Income (Loss)	$ 333	$ (23)