Investment in Unconsolidated Joint Ventures (Summary of Financial Data and Principal Activities) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
SUMMARY OF FINANCIAL POSITION:
Total Assets	$ 809,606		$ 930,904
Total Debt	444,760		526,458
Total Equity	324,444		366,113
Company’s Investment	86,740		156,388
SUMMARY OF OPERATIONS:
Total Revenues	86,089	$ 79,361
Net Income (Loss)	74,055	17,606
Company's Share of Income (Loss)	43,362	5,144
Terminus Office Holdings
SUMMARY OF FINANCIAL POSITION:
Total Assets	268,531		268,242
Total Debt	204,390		207,545
Total Equity	50,633		49,476
Company’s Investment	26,204		25,686
SUMMARY OF OPERATIONS:
Total Revenues	33,503	31,630
Net Income (Loss)	4,907	3,874
Company's Share of Income (Loss)	2,453	1,937
EP I LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	1,517		78,537
Total Debt	0		58,029
Total Equity	1,269		18,962
Company’s Investment	738		18,551
SUMMARY OF OPERATIONS:
Total Revenues	4,094	7,919
Net Income (Loss)	44,865	1,417
Company's Share of Income (Loss)	28,479	1,206
EP II LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	392		67,754
Total Debt	0		44,969
Total Equity	296		21,743
Company’s Investment	130		17,606
SUMMARY OF OPERATIONS:
Total Revenues	2,644	3,605
Net Income (Loss)	13,023	(1,194)
Company's Share of Income (Loss)	9,768	(1,043)
Charlotte Gateway Village, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	129,109		119,054
Total Debt	0		0
Total Equity	124,012		116,809
Company’s Investment	15,397		11,796
SUMMARY OF OPERATIONS:
Total Revenues	20,125	26,245
Net Income (Loss)	7,202	11,077
Company's Share of Income (Loss)	3,601	1,447
HICO Victory Center LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	14,294		14,124
Total Debt	0		0
Total Equity	14,290		13,869
Company’s Investment	9,695		9,506
SUMMARY OF OPERATIONS:
Total Revenues	320	307
Net Income (Loss)	320	300
Company's Share of Income (Loss)	171	131
Carolina Square Holdings LP
SUMMARY OF FINANCIAL POSITION:
Total Assets	102,370		66,922
Total Debt	62,180		23,741
Total Equity	34,080		34,173
Company’s Investment	18,843		18,325
SUMMARY OF OPERATIONS:
Total Revenues	640	0
Net Income (Loss)	(100)	0
Company's Share of Income (Loss)	19	0
CL Realty, L.L.C.
SUMMARY OF FINANCIAL POSITION:
Total Assets	8,287		8,047
Total Debt	0		0
Total Equity	8,156		7,899
Company’s Investment	2,852		3,644
SUMMARY OF OPERATIONS:
Total Revenues	2,899	327
Net Income (Loss)	2,657	105
Company's Share of Income (Loss)	408	70
DC Charlotte Plaza LLLP
SUMMARY OF FINANCIAL POSITION:
Total Assets	39,156		17,940
Total Debt	0		0
Total Equity	34,255		17,073
Company’s Investment	17,475		8,937
SUMMARY OF OPERATIONS:
Total Revenues	2	47
Net Income (Loss)	2	45
Company's Share of Income (Loss)	1	24
Temco Associates, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	4,426		4,368
Total Debt	0		0
Total Equity	4,323		4,253
Company’s Investment	864		829
SUMMARY OF OPERATIONS:
Total Revenues	144	180
Net Income (Loss)	70	83
Company's Share of Income (Loss)	35	122
Wildwood Associates
SUMMARY OF FINANCIAL POSITION:
Total Assets	16,368		16,351
Total Debt	0		0
Total Equity	16,227		16,314
Company’s Investment	(1,186)		(1,143)
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	(86)	(106)
Company's Share of Income (Loss)	(43)	(53)
Crawford Long - CPI, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	28,621		27,523
Total Debt	71,690		72,822
Total Equity	(44,787)		(45,928)
Company’s Investment	(21,296)		(21,866)
SUMMARY OF OPERATIONS:
Total Revenues	9,017	9,101
Net Income (Loss)	2,285	2,005
Company's Share of Income (Loss)	1,142	1,003
111 West Rio Building
SUMMARY OF FINANCIAL POSITION:
Total Assets	0		59,399
Total Debt	0		12,852
Total Equity	0		32,855
Company’s Investment	0		52,206
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	0	0
Company's Share of Income (Loss)	(2,592)	0
Courvoisier Centre JV, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	182,262		172,197
Total Debt	106,500		106,500
Total Equity	68,480		69,479
Company’s Investment	11,719		11,782
SUMMARY OF OPERATIONS:
Total Revenues	12,701	0
Net Income (Loss)	(1,000)	0
Company's Share of Income (Loss)	(80)	0
HICO Avalon II, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	987		0
Total Debt	0		0
Total Equity	532		0
Company’s Investment	4,366		0
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	(68)	0
Company's Share of Income (Loss)	0	0
AMCO 120 WT Holdings, LLC
SUMMARY OF FINANCIAL POSITION:
Total Assets	13,286		10,446
Total Debt	0		0
Total Equity	12,678		9,136
Company’s Investment	939		184
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	(22)	0
Company's Share of Income (Loss)	0	0
Other
SUMMARY OF FINANCIAL POSITION:
Total Assets	0		0
Total Debt	0		0
Total Equity	0		0
Company’s Investment	0		$ 345
SUMMARY OF OPERATIONS:
Total Revenues	0	0
Net Income (Loss)	0	0
Company's Share of Income (Loss)	$ 0	$ 300