Investment in Unconsolidated Joint Ventures (Details)			1 Months Ended	9 Months Ended
		Oct. 06, 2016 ft² $ / shares shares	Nov. 01, 2016 $ / shares shares	Sep. 30, 2016 USD ($) ft² condominium_unit shares	Sep. 30, 2015 USD ($)	Oct. 20, 2016 USD ($)	Oct. 17, 2016 ft²	Dec. 31, 2015 USD ($) ft²
Schedule of Equity Method Investments [Line Items]
Document Period End Date				Sep. 30, 2016
Document Fiscal Year Focus				2016
SUMMARY OF FINANCIAL POSITION:
Total Assets				$ 691,409,000				$ 644,880,000
Total Debt				397,082,000				401,977,000
Total Equity				263,579,000				219,079,000
Company's Investment				93,572,000				$ 79,434,000
SUMMARY OF OPERATIONS:
Total Revenues				79,361,000	$ 84,608,000
Net Income (Loss)				17,606,000	18,062,000
Income (Loss) from Equity Method Investments Gross of Impairment Charges				$ 5,144,000	7,088,000
Area of Real Estate Property | ft²				1,200,000				129,000
Terminus Office Holdings [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				$ 274,417,000				$ 277,444,000
Total Debt				208,572,000				211,216,000
Total Equity				52,743,000				56,369,000
Company's Investment				27,381,000				29,110,000
SUMMARY OF OPERATIONS:
Total Revenues				31,630,000	30,144,000
Net Income (Loss)				3,874,000	1,923,000
Income (Loss) from Equity Method Investments Gross of Impairment Charges				1,937,000	962,000
EP I LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				81,204,000				83,115,000
Total Debt				58,029,000				58,029,000
Total Equity				21,006,000				24,172,000
Company's Investment				19,753,000				21,502,000
SUMMARY OF OPERATIONS:
Total Revenues				7,919,000	9,587,000
Net Income (Loss)				1,417,000	2,481,000
Income (Loss) from Equity Method Investments Gross of Impairment Charges				1,206,000	1,864,000
EP II LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				68,179,000				70,704,000
Total Debt				44,736,000				40,910,000
Total Equity				22,136,000				24,331,000
Company's Investment				17,892,000				19,118,000
SUMMARY OF OPERATIONS:
Total Revenues				3,605,000	536,000
Net Income (Loss)				(1,194,000)	(150,000)
Income (Loss) from Equity Method Investments Gross of Impairment Charges				(1,043,000)	(100,000)
Charlotte Gateway Village, LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				120,828,000				123,531,000
Total Debt				3,265,000				17,536,000
Total Equity				114,038,000				104,336,000
Company's Investment				11,359,000				11,190,000
SUMMARY OF OPERATIONS:
Total Revenues				26,245,000	25,311,000
Net Income (Loss)				11,077,000	9,438,000
Income (Loss) from Equity Method Investments Gross of Impairment Charges				1,447,000	883,000
HICO Victory Center LP [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				13,798,000				13,532,000
Total Debt				0				0
Total Equity				13,793,000				13,229,000
Company's Investment				9,419,000				9,138,000
SUMMARY OF OPERATIONS:
Total Revenues				307,000	0
Net Income (Loss)				300,000	0
Income (Loss) from Equity Method Investments Gross of Impairment Charges				131,000	0
Temco Associates, LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				5,324,000				5,284,000
Total Debt				0				0
Total Equity				5,196,000				5,133,000
Company's Investment				1,100,000				977,000
SUMMARY OF OPERATIONS:
Total Revenues				180,000	9,163,000
Net Income (Loss)				83,000	2,077,000
Income (Loss) from Equity Method Investments Gross of Impairment Charges				122,000	2,244,000
Carolina Square Holdings LP [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				51,507,000				15,729,000
Total Debt				9,287,000				0
Total Equity				34,164,000				12,085,000
Company's Investment				18,256,000				6,782,000
CL Realty, L.L.C. [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				7,869,000				7,872,000
Total Debt				0				0
Total Equity				7,767,000				7,662,000
Company's Investment				3,585,000				3,515,000
SUMMARY OF OPERATIONS:
Total Revenues				327,000	674,000
Net Income (Loss)				105,000	346,000
Income (Loss) from Equity Method Investments Gross of Impairment Charges				70,000	178,000
Wildwood Associates
SUMMARY OF FINANCIAL POSITION:
Total Assets				16,378,000				16,419,000
Total Debt				0				0
Total Equity				16,298,000				16,354,000
Company's Investment	[1]				(1,125,000)			(1,122,000)
SUMMARY OF OPERATIONS:
Total Revenues				0	0
Net Income (Loss)				(106,000)	(89,000)
Income (Loss) from Equity Method Investments Gross of Impairment Charges				(53,000)	(45,000)
Crawford Long CPI LLC [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				28,449,000				29,143,000
Total Debt				73,193,000				74,286,000
Total Equity				(46,667,000)				(46,238,000)
Company's Investment	[1]			(22,236,000)				(22,021,000)
SUMMARY OF OPERATIONS:
Total Revenues				9,101,000	9,193,000
Net Income (Loss)				2,005,000	2,131,000
Income (Loss) from Equity Method Investments Gross of Impairment Charges				$ 1,003,000	1,071,000
AMCO 120 WT Holdings, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage of Partner in Joint Venture				20.00%
SUMMARY OF FINANCIAL POSITION:
Total Assets				$ 8,288,000				0
Total Debt				0				0
Total Equity				7,941,000				0
Company's Investment				0				0
Other Equity Method Investee [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				0				2,107,000
Total Debt				0				0
Total Equity				0				1,646,000
Company's Investment				0				1,245,000
SUMMARY OF OPERATIONS:
Total Revenues				0	0
Net Income (Loss)				0	(95,000)
Income (Loss) from Equity Method Investments Gross of Impairment Charges				300,000	31,000
DC Charlotte Plaza LLLP [Member]
SUMMARY OF FINANCIAL POSITION:
Total Assets				15,168,000				0
Total Debt				0				0
Total Equity				15,164,000				0
Company's Investment				8,188,000				$ 0
SUMMARY OF OPERATIONS:
Total Revenues				47,000	0
Net Income (Loss)				45,000	0
Income (Loss) from Equity Method Investments Gross of Impairment Charges				$ 24,000	$ 0
Area of Real Estate Property | ft²				282,000
AMLI Residential [Member] | AMCO 120 WT Holdings, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage of Partner in Joint Venture				80.00%
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%
Officer [Member] | AMCO 120 WT Holdings, LLC [Member]
SUMMARY OF OPERATIONS:
Area of Real Estate Property | ft²				30,000
Retail Segment [Member] | AMCO 120 WT Holdings, LLC [Member]
SUMMARY OF OPERATIONS:
Area of Real Estate Property | ft²				10,000
Residential Real Estate [Member] | AMCO 120 WT Holdings, LLC [Member]
SUMMARY OF OPERATIONS:
Number of Units in Real Estate Property | condominium_unit				330
Restricted Stock [Member]
Schedule of Equity Method Investments [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | shares				234,965
Subsequent Event [Member]
SUMMARY OF OPERATIONS:
Area of Real Estate Property | ft²							941,000
Subsequent Event [Member] | 111 West Rio [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage of Partner in Joint Venture		74.60%
SUMMARY OF OPERATIONS:
Area of Real Estate Property | ft²		229,000
Business Combination Purchase Price						$ 19,600,000
Subsequent Event [Member] | Limited Partner [Member] | 111 West Rio [Member]
Schedule of Equity Method Investments [Line Items]
Ownership Percentage of Partner in Joint Venture		25.40%
Subsequent Event [Member] | Restricted Stock [Member]
Schedule of Equity Method Investments [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | shares		377,610	498,325
Subsequent Event [Member] | Restricted Stock Units (RSUs) [Member]
Schedule of Equity Method Investments [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | shares		981,612	1,295,417
Subsequent Event [Member] | Option on Securities [Member]
Schedule of Equity Method Investments [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period | shares		1,730,981	2,284,346
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Period Increase (Decrease), Weighted Average Exercise Price | $ / shares		$ 21.99	$ 16.66
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures | shares		672,375
Investment Options, Exercise Price | $ / shares			$ 7.82

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