Investment in Unconsolidated Joint Ventures (Summary of Financial Position) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Total Assets	$ 690,893	$ 643,134
Total Debt	343,149	338,590
Total Equity	314,879	267,423
Company’s Investment	122,961	78,940
Terminus Office Holdings
Schedule of Equity Method Investments [Line Items]
Total Assets	259,812	261,999
Total Debt	202,051	203,131
Total Equity	46,632	48,033
Company’s Investment	46,583	24,898
DC Charlotte Plaza LLLP
Schedule of Equity Method Investments [Line Items]
Total Assets	65,588	53,791
Total Debt	0	0
Total Equity	55,121	42,853
Company’s Investment	28,544	22,293
Carolina Square Holdings LP
Schedule of Equity Method Investments [Line Items]
Total Assets	107,975	106,580
Total Debt	70,426	64,412
Total Equity	33,850	33,648
Company’s Investment	19,235	19,384
Charlotte Gateway Village, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	127,198	124,691
Total Debt	0	0
Total Equity	123,674	121,386
Company’s Investment	15,459	14,568
Austin 300 Colorado Project, LP
Schedule of Equity Method Investments [Line Items]
Total Assets	32,896	0
Total Debt	0	0
Total Equity	32,846	0
Company’s Investment	14,606	0
HICO Victory Center LP
Schedule of Equity Method Investments [Line Items]
Total Assets	14,500	14,403
Total Debt	0	0
Total Equity	14,497	14,401
Company’s Investment	9,803	9,752
HICO Avalon II, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	6,570	6,379
Total Debt	0	0
Total Equity	6,540	6,303
Company’s Investment	5,104	4,931
CL Realty, L.L.C.
Schedule of Equity Method Investments [Line Items]
Total Assets	8,114	8,287
Total Debt	0	0
Total Equity	8,056	8,127
Company’s Investment	2,953	2,980
AMCO 120 WT Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	20,879	18,066
Total Debt	0	0
Total Equity	18,972	16,354
Company’s Investment	2,239	1,664
Temco Associates, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	4,470	4,441
Total Debt	0	0
Total Equity	4,367	4,337
Company’s Investment	886	875
EP II LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	270	277
Total Debt	0	0
Total Equity	175	180
Company’s Investment	40	44
EP I LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	498	521
Total Debt	0	0
Total Equity	303	319
Company’s Investment	13	25
Wildwood Associates
Schedule of Equity Method Investments [Line Items]
Total Assets	14,884	16,337
Total Debt	0	0
Total Equity	14,828	16,297
Company’s Investment	(1,077)	(1,151)
Crawford Long - CPI, LLC
Schedule of Equity Method Investments [Line Items]
Total Assets	27,239	27,362
Total Debt	70,672	71,047
Total Equity	(44,982)	(44,815)
Company’s Investment	$ (21,427)	$ (21,323)