Investment in Unconsolidated Joint Ventures (Summary of Financial Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Total Assets	$ 707,033	$ 643,134
Total Debt	344,390	338,590
Total Equity	316,839	267,423
Company’s Investment	121,423	78,940
Terminus Office Holdings
Schedule of Equity Method Investments [Line Items]
Total Assets	259,619	261,999
Total Debt	200,957	203,131
Total Equity	48,103	48,033
Company’s Investment	47,349	24,898
DC Charlotte Plaza LLLP
Schedule of Equity Method Investments [Line Items]
Total Assets	98,068	53,791
Total Debt	0	0
Total Equity	72,225	42,853
Company’s Investment	35,647	22,293
Carolina Square Holdings LP
Schedule of Equity Method Investments [Line Items]
Total Assets	108,915	106,580
Total Debt	73,140	64,412
Total Equity	34,093	33,648
Company’s Investment	19,450	19,384
Charlotte Gateway Village, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	115,244	124,691
Total Debt	0	0
Total Equity	110,570	121,386
Company’s Investment	8,677	14,568
Austin 300 Colorado Project, LP
Schedule of Equity Method Investments [Line Items]
Total Assets	33,630	0
Total Debt	0	0
Total Equity	33,569	0
Company’s Investment	15,483	0
HICO Victory Center LP
Schedule of Equity Method Investments [Line Items]
Total Assets	14,734	14,403
Total Debt	0	0
Total Equity	14,603	14,401
Company’s Investment	9,865	9,752
CL Realty, L.L.C.
Schedule of Equity Method Investments [Line Items]
Total Assets	8,098	8,287
Total Debt	0	0
Total Equity	8,029	8,127
Company’s Investment	2,932	2,980
AMCO 120 WT Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	24,384	18,066
Total Debt	0	0
Total Equity	24,407	16,354
Company’s Investment	2,853	1,664
Temco Associates, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	4,485	4,441
Total Debt	0	0
Total Equity	4,380	4,337
Company’s Investment	896	875
EP II LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	260	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	315	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	11,228	16,337
Total Debt	0	0
Total Equity	11,162	16,297
Company’s Investment	(433)	(1,151)
Crawford Long - CPI, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	27,867	27,362
Total Debt	70,293	71,047
Total Equity	(44,777)	(44,815)
Company’s Investment	$ (21,345)	$ (21,323)