REAL ESTATE (Schedule of Real Estate Investments) (Details) (USD $) In Thousands, unless otherwise specified				3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Office [Member]	Mar. 31, 2014 Domain Gateway [Member] Office [Member]	Mar. 31, 2014 Town Center [Member] Office [Member]	Mar. 31, 2014 McEwen Building [Member] Office [Member]	Mar. 31, 2014 Gateway Tech Center [Member] Office [Member]	Mar. 31, 2014 Tower on Lake Carolyn [Member] Office [Member]	Mar. 31, 2014 RBC Plaza [Member] Office [Member]	Mar. 31, 2014 One Washingtonian Center [Member] Office [Member]	Mar. 31, 2014 Preston Commons [Member] Office [Member]	Mar. 31, 2014 Sterling Plaza [Member] Office [Member]	Mar. 31, 2014 201 Spear Street [Member] Office [Member]	Mar. 31, 2014 500 West Madison [Member] Office [Member]	Mar. 31, 2014 222 Main [Member] Office [Member]
Real Estate Properties [Line Items]
Date Acquired				Sep. 29, 2011	Mar. 27, 2012	Apr. 30, 2012	May 09, 2012	Dec. 21, 2012	Jan. 31, 2013	Jun. 19, 2013	Jun. 19, 2013	Jun. 19, 2013	Dec. 03, 2013	Dec. 16, 2013	Feb. 27, 2014
Total Real Estate at Cost	$ 1,404,652	$ 1,240,928	$ 1,404,652	$ 47,374	$ 118,637	$ 40,326	$ 29,483	$ 48,701	$ 129,064	$ 88,929	$ 116,043	$ 76,982	$ 126,630	$ 419,941	$ 162,542
Accumulated Depreciation and Amortization	(57,407)	(42,044)	(57,407)	(5,468)	(12,399)	(4,145)	(3,107)	(4,064)	(7,955)	(3,551)	(4,809)	(3,554)	(1,424)	(6,391)	(540)
Total real estate held for investment, net	$ 1,347,245	$ 1,198,884	$ 1,347,245	$ 41,906	$ 106,238	$ 36,181	$ 26,376	$ 44,637	$ 121,109	$ 85,378	$ 111,234	$ 73,428	$ 125,206	$ 413,550	$ 162,002