INVESTMENT IN UNCONSOLIDATED JOINT VENTURES (Summarized Financial Information - 110 William Joint Venture) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Balance Sheet Related Disclosures [Abstract]
Real estate assets, net of accumulated depreciation and amortization		$ 840,423		$ 840,423		$ 847,734
Total assets		1,024,887		1,024,887		1,022,514
Other liabilities		9,445		9,445		9,192
Total Liabilities and Equity		1,024,887		1,024,887		1,022,514
Balance outstanding		539,928		539,928
Income Statement [Abstract]
Revenues		28,667	$ 26,244	56,610	$ 50,871
Operating, maintenance, and management		8,980	8,578	17,924	17,293
Real estate taxes and insurance		3,839	3,426	7,498	6,920
Real estate acquisition fees and expenses		0	4	0	2,180
Depreciation and amortization		11,159	11,883	22,387	23,614
Interest expense		3,857	4,595	7,769	8,028
Total expenses		30,781	31,373	61,440	65,716
Net income (loss) attributable to common stockholders		1,526	(5,331)	3,761	(14,948)
Company's equity in loss of unconsolidated joint venture		(118)	(333)	(336)	(501)
Mortgages [Member] | First Mortgage Loan [Member]
Balance Sheet Related Disclosures [Abstract]
Balance outstanding		139,600		$ 139,600		140,700
Basis spread on variable rate	[1],[2]			4.80%
Mortgages [Member] | Mezzanine Loan [Member]
Balance Sheet Related Disclosures [Abstract]
Balance outstanding		20,000		$ 20,000		20,000
Basis spread on variable rate	[1],[2]			9.50%
Notes Payable [Member]
Balance Sheet Related Disclosures [Abstract]
Unamortized premium		6,000		$ 6,000		7,500
110 William Joint Venture [Member]
Balance Sheet Related Disclosures [Abstract]
Real estate assets, net of accumulated depreciation and amortization		272,723		272,723		276,683
Other assets		17,394		17,394		15,858
Total assets		290,117		290,117		292,541
Notes payable, net	[3]	165,645		165,645		168,178
Other liabilities		13,629		13,629		15,796
Partners’ capital		110,843		110,843		108,567
Total Liabilities and Equity		290,117		290,117		$ 292,541
Income Statement [Abstract]
Revenues		8,413	5,448	16,698	5,448
Operating, maintenance, and management		2,784	1,389	5,487	1,389
Real estate taxes and insurance		1,352	849	2,687	849
Real estate acquisition fees and expenses		0	711	0	991
Depreciation and amortization		3,222	2,056	6,282	2,056
Interest expense		1,542	1,031	3,075	1,031
Total expenses		8,900	6,036	17,531	6,316
Other income		307	33	308	33
Net income (loss) attributable to common stockholders		(180)	(555)	(525)	(835)
Company's equity in loss of unconsolidated joint venture		$ (118)	$ (333)	$ (336)	$ (501)

[1] Contractual interest rate represents the interest rate in effect under the loan as of June 30, 2015. Effective interest rate is calculated as the actual interest rate in effect as of June 30, 2015 (consisting of the contractual interest rate and contractual floor rates), using interest rate indices at June 30, 2015, where applicable.

[2] The Portfolio Revolving Loan Facility is secured by the 1800 West Loop Building and the Iron Point Business Park. The Portfolio Revolving Loan Facility is comprised of $59.5 million of revolving debt and $13.0 million of non-revolving debt available to be used for tenant improvements, leasing commissions and capital improvements, subject to certain terms and conditions contained in the loan documents. As of June 30, 2015, $30.0 million of revolving debt and $9.8 million of non-revolving debt had been disbursed to the Company and the remaining $29.5 million of revolving debt and $3.2 million of non-revolving debt is available for future disbursements, subject to certain conditions contained in the loan documents. Monthly payments are initially interest only. Beginning June 1, 2016, and to the extent that there are amounts outstanding under the non-revolving portion of the loan, monthly payments will include interest and principal amortization payments of up to $80,000 per month.

[3] Includes (i) a first mortgage loan with an outstanding principal balance of $139.6 million and $140.7 million as of June 30, 2015 and December 31, 2014, respectively, bearing interest at a fixed rate of 4.8% per annum and maturing on July 6, 2017 and (ii) a mezzanine loan with an outstanding principal balance of $20.0 million as of June 30, 2015 and December 31, 2014 bearing interest at a fixed rate of 9.5% per annum and maturing on July 6, 2017. The amount presented is net of a premium on notes payable of $6.0 million and $7.5 million as of June 30, 2015 and December 31, 2014, respectively.