Investment in Unconsolidated Joint Ventures (Summary of Financial Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Total Assets	$ 746,718	$ 643,134
Total Debt	343,755	338,590
Total Equity	330,757	267,423
Company’s Investment	132,368	78,940
Terminus Office Holdings
Schedule of Equity Method Investments [Line Items]
Total Assets	260,668	261,999
Total Debt	199,851	203,131
Total Equity	49,458	48,033
Company’s Investment	48,019	24,898
DC Charlotte Plaza LLLP
Schedule of Equity Method Investments [Line Items]
Total Assets	129,916	53,791
Total Debt	0	0
Total Equity	84,385	42,853
Company’s Investment	43,656	22,293
Austin 300 Colorado Project, LP
Schedule of Equity Method Investments [Line Items]
Total Assets	39,467	0
Total Debt	0	0
Total Equity	37,187	0
Company’s Investment	19,180	0
Carolina Square Holdings LP
Schedule of Equity Method Investments [Line Items]
Total Assets	109,830	106,580
Total Debt	73,993	64,412
Total Equity	34,305	33,648
Company’s Investment	16,943	19,384
HICO Victory Center LP
Schedule of Equity Method Investments [Line Items]
Total Assets	14,857	14,403
Total Debt	0	0
Total Equity	14,683	14,401
Company’s Investment	9,925	9,752
Charlotte Gateway Village, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	115,071	124,691
Total Debt	0	0
Total Equity	110,172	121,386
Company’s Investment	8,478	14,568
AMCO 120 WT Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	28,791	18,066
Total Debt	0	0
Total Equity	24,878	16,354
Company’s Investment	4,004	1,664
CL Realty, L.L.C.
Schedule of Equity Method Investments [Line Items]
Total Assets	4,342	8,287
Total Debt	0	0
Total Equity	4,228	8,127
Company’s Investment	2,909	2,980
Temco Associates, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	4,506	4,441
Total Debt	0	0
Total Equity	4,402	4,337
Company’s Investment	907	875
EP II LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	254	277
Total Debt	0	0
Total Equity	160	180
Company’s Investment	28	44
EP I LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	501	521
Total Debt	0	0
Total Equity	320	319
Company’s Investment	21	25
HICO Avalon II, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	0	6,379
Total Debt	0	0
Total Equity	0	6,303
Company’s Investment	0	4,931
Wildwood Associates
Schedule of Equity Method Investments [Line Items]
Total Assets	11,219	16,337
Total Debt	0	0
Total Equity	11,140	16,297
Company’s Investment	(444)	(1,151)
Crawford Long - CPI, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	27,296	27,362
Total Debt	69,911	71,047
Total Equity	(44,561)	(44,815)
Company’s Investment	$ (21,258)	$ (21,323)