Investment in Unconsolidated Joint Ventures (Details) $ in Thousands		6 Months Ended
		Jun. 30, 2016 USD ($) ft²	Jun. 30, 2015 USD ($)	Mar. 31, 2016 ft²	Dec. 31, 2015 USD ($)
Schedule of Equity Method Investments [Line Items]
Document Period End Date		Jun. 30, 2016
Document Fiscal Year Focus		2016
SUMMARY OF FINANCIAL POSITION:
Total Assets		$ 667,328			$ 644,880
Total Debt		393,772			401,977
Total Equity		244,597			219,079
Company's Investment		91,145			79,434
SUMMARY OF OPERATIONS:
Total Revenues		53,080	$ 50,533
Net Income (Loss)		11,638	10,729
Income (Loss) from Equity Method Investments Gross of Impairment Charges		3,618	3,372
Area of Real Estate Property | ft²				129,000
Terminus Office Holdings [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		273,890			277,444
Total Debt		209,588			211,216
Total Equity		51,466			56,369
Company's Investment		26,631			29,110
SUMMARY OF OPERATIONS:
Total Revenues		20,978	19,638
Net Income (Loss)		2,597	1,139
Income (Loss) from Equity Method Investments Gross of Impairment Charges		1,298	570
EP I LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		81,838			83,115
Total Debt		58,030			58,029
Total Equity		21,716			24,172
Company's Investment		20,218			21,502
SUMMARY OF OPERATIONS:
Total Revenues		5,991	6,218
Net Income (Loss)		1,168	1,480
Income (Loss) from Equity Method Investments Gross of Impairment Charges		951	1,112
EP II LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		68,926			70,704
Total Debt		44,494			40,910
Total Equity		22,913			24,331
Company's Investment		18,144			19,118
SUMMARY OF OPERATIONS:
Total Revenues		2,044	0
Net Income (Loss)		(1,018)	0
Income (Loss) from Equity Method Investments Gross of Impairment Charges		(823)	0
Charlotte Gateway Village, LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		121,452			123,531
Total Debt		8,099			17,536
Total Equity		110,502			104,336
Company's Investment		11,190			11,190
SUMMARY OF OPERATIONS:
Total Revenues		17,477	16,913
Net Income (Loss)		7,263	6,225
Income (Loss) from Equity Method Investments Gross of Impairment Charges		987	589
HICO Victory Center LP [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		13,661			13,532
Total Debt		0			0
Total Equity		13,656			13,229
Company's Investment		9,365			9,138
SUMMARY OF OPERATIONS:
Total Revenues		169	0
Net Income (Loss)		162	0
Income (Loss) from Equity Method Investments Gross of Impairment Charges		81	0
Temco Associates, LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		5,311			5,284
Total Debt		0			0
Total Equity		5,192			5,133
Company's Investment		1,097			977
SUMMARY OF OPERATIONS:
Total Revenues		147	1,144
Net Income (Loss)		79	435
Income (Loss) from Equity Method Investments Gross of Impairment Charges		119	242
Carolina Square Holdings LP [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		34,386			15,729
Total Debt		0			0
Total Equity		27,890			12,085
Company's Investment		16,874			6,782
CL Realty, L.L.C. [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		7,829			7,872
Total Debt		0			0
Total Equity		7,726			7,662
Company's Investment		3,560			3,515
SUMMARY OF OPERATIONS:
Total Revenues		246	469
Net Income (Loss)		64	243
Income (Loss) from Equity Method Investments Gross of Impairment Charges		44	130
Wildwood Associates
SUMMARY OF FINANCIAL POSITION:
Total Assets		16,337			16,419
Total Debt		0			0
Total Equity		16,298			16,354
Company's Investment	[1]		(1,150)		(1,122)
SUMMARY OF OPERATIONS:
Total Revenues		0	0
Net Income (Loss)		(56)	(58)
Income (Loss) from Equity Method Investments Gross of Impairment Charges		(28)	(30)
Crawford Long CPI LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		29,405			29,143
Total Debt		73,561			74,286
Total Equity		(46,516)			(46,238)
Company's Investment	[1]	(22,160)			(22,021)
SUMMARY OF OPERATIONS:
Total Revenues		6,028	6,139
Net Income (Loss)		1,346	1,446
Income (Loss) from Equity Method Investments Gross of Impairment Charges		673	728
Other Equity Method Investee [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		0			2,107
Total Debt		0			0
Total Equity		0			1,646
Company's Investment		0			1,245
SUMMARY OF OPERATIONS:
Total Revenues		0	12
Net Income (Loss)		0	(181)
Income (Loss) from Equity Method Investments Gross of Impairment Charges		298	31
DC Charlotte Plaza LLLP [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets		14,293			0
Total Debt		0			0
Total Equity		13,754			0
Company's Investment		7,376			$ 0
SUMMARY OF OPERATIONS:
Total Revenues		0	0
Net Income (Loss)		33	0
Income (Loss) from Equity Method Investments Gross of Impairment Charges		$ 18	$ 0
Dimensional Fund Advisors [Member] | DC Charlotte Plaza LLLP [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage of Partner in Joint Venture		5000.00%
DC Charlotte Plaza LLLP [Member]
SUMMARY OF OPERATIONS:
Area of Real Estate Property | ft²		229,000

[1] Negative balances are included in deferred income on the balance sheets.