Investment in Unconsolidated Joint Ventures (Summary of Financial Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
SUMMARY OF FINANCIAL POSITION
Total Assets	$ 658,303	$ 779,204
Total Debt	165,039	342,892
Total Equity (Deficit)	354,404	338,427
Company's Investment	114,158	140,376
DC Charlotte Plaza LLLP
SUMMARY OF FINANCIAL POSITION
Total Assets	179,694	155,530
Total Debt	0	0
Total Equity (Deficit)	90,373	88,922
Company's Investment	48,058	46,554
Austin 300 Colorado Project, LP
SUMMARY OF FINANCIAL POSITION
Total Assets	112,630	51,180
Total Debt	21,430	0
Total Equity (Deficit)	68,101	41,298
Company's Investment	36,846	22,335
Carolina Square Holdings LP
SUMMARY OF FINANCIAL POSITION
Total Assets	114,483	106,187
Total Debt	75,662	74,638
Total Equity (Deficit)	25,184	28,844
Company's Investment	14,414	16,840
AMCO 120 WT Holdings, LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	77,377	36,680
Total Debt	0	0
Total Equity (Deficit)	70,696	31,372
Company's Investment	13,362	5,538
HICO Victory Center LP
SUMMARY OF FINANCIAL POSITION
Total Assets	16,045	15,069
Total Debt	0	0
Total Equity (Deficit)	15,353	14,801
Company's Investment	10,373	10,003
Charlotte Gateway Village, LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	109,675	112,553
Total Debt	0	0
Total Equity (Deficit)	106,651	109,666
Company's Investment	6,718	8,225
Terminus Office Holdings LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	0	258,060
Total Debt	0	198,732
Total Equity (Deficit)	0	50,539
Company's Investment	0	48,571
Wildwood Associates
SUMMARY OF FINANCIAL POSITION
Total Assets	11,061	11,157
Total Debt	0	0
Total Equity (Deficit)	10,978	11,108
Company's Investment	(521)	(460)
Crawford Long - CPI, LLC
SUMMARY OF FINANCIAL POSITION
Total Assets	28,459	26,429
Total Debt	67,947	69,522
Total Equity (Deficit)	(40,250)	(44,146)
Company's Investment	(19,205)	(21,071)
Other
SUMMARY OF FINANCIAL POSITION
Total Assets	8,879	6,359
Total Debt	0	0
Total Equity (Deficit)	7,318	6,023
Company's Investment	$ 4,113	$ 3,841