Acquisitions, Dispositions, Leasing and Financing Activities - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended			9 Months Ended	1 Months Ended		9 Months Ended						9 Months Ended		1 Months Ended	3 Months Ended		1 Months Ended				1 Months Ended		1 Months Ended		1 Months Ended						3 Months Ended	9 Months Ended	1 Months Ended		1 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended
	Jun. 01, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Churchill [Member]	Mar. 31, 2013 Playa Vista Mezzanine Loan [Member]	Jan. 31, 2013 Playa Vista Mezzanine Loan [Member] sqft	Sep. 30, 2013 Playa Vista Mezzanine Loan [Member]	Feb. 28, 2013 Playa Vista Mezzanine Loan [Member]	Jan. 24, 2013 Playa Vista Mezzanine Loan [Member]	Sep. 30, 2013 Recourse Secured Financings [Member]	Jun. 30, 2013 Recourse Secured Financings [Member]	Dec. 31, 2012 Recourse Secured Financings [Member]	Sep. 30, 2013 1515 Market Street [Member]	Jan. 31, 2013 1515 Market Street [Member]	Jun. 11, 2013 Deer Valley [Member]	Sep. 30, 2013 701 Seventh Avenue [Member]	Jul. 09, 2013 701 Seventh Avenue [Member]	Aug. 31, 2012 10 Metrotech Loan LLC [Member]	Sep. 30, 2013 10 Metrotech Loan LLC [Member]	Jul. 30, 2013 10 Metrotech Loan LLC [Member]	Dec. 31, 2012 10 Metrotech Loan LLC [Member]	Aug. 21, 2013 WRT-Elad One South State Lender LP [Member]	Sep. 30, 2013 WRT-Elad One South State Lender LP [Member]	Oct. 31, 2013 Subsequent Event [Member] 701 Seventh Avenue [Member]	Aug. 21, 2013 Mezzanine [Member] WRT-Elad One South State Lender LP [Member]	Jul. 02, 2013 Denton Property Sale [Member]	Aug. 01, 2013 Seabrook Property Sale [Member]	Mar. 28, 2013 Residential [Member]	Aug. 13, 2013 Residential [Member]	Oct. 07, 2013 Residential [Member] Subsequent Event [Member]	Jun. 28, 2013 First Mortgage [Member] Churchill [Member]	Sep. 30, 2013 Queensridge [Member]	Sep. 30, 2013 Queensridge [Member]	Apr. 30, 2013 1515 Market Street Loan Modification [Member] Original Mortgage [Member]	Apr. 25, 2013 1515 Market Street Loan Modification [Member] Original Mortgage [Member]	Apr. 30, 2013 1515 Market Street Loan Modification [Member] First Mortgage [Member]	Apr. 25, 2013 1515 Market Street Loan Modification [Member] First Mortgage [Member]	Jun. 20, 2013 Atrium Property [Member]	Jun. 30, 2013 Atrium Property [Member]	Sep. 30, 2013 Atrium Property [Member] Times sqft
Loans At Acquisition Date [Line Items]
Increased outstanding principal amount																	$ 71,629,000
Maturity date of loan																	Feb. 01, 2016
Mortgage loans on real estate adjusted interest rate minimum																	7.50%
LIBOR plus																	6.50%
Increased loan balance through future funding advances																	6,000,000
Future advances																	500,000
First mortgage loan of Trust										80,300,000							70,000,000																	5,100,000						43,000,000
Interest rate increase for each future advances																	0.10%
Percentage for participation																	40.00%																					40.00%
Acquired interest rate through indirect																	49.00%																					49.00%
Payment to acquire indirect interest																10,000
Aggregate investment		139,061,000		139,061,000		134,859,000														120,000,000		11,000		10,845,000
Additional contribution	5,850,000			11,982,000	47,925,000														5,403,000								16,686,000
Reduction of future funding commitments																											67,198,000
Aggregate purchase price		380,240,000		380,240,000		378,737,000																										246,000,000
Non-refundable deposits																																25,500,000	7,500,000
Gross proceeds from sales																		20,500,000											1,850,000	3,300,000	12,000,000
Net proceeds																		19,585,000											1,703,000		11,425,000
Gain on sale of property		1,421,000	945,000	10,948,000	945,000													6,752,000											0	1,428,000	2,775,000
Net proceeds				36,217,000	7,024,000																									3,202,000
Amount of non-performing mortgage loan acquired																																						33,157,000			10,650,000		10,650,000
Non-performing mortgage loan acquisition cost				21,437,000	64,970,000																																				6,625,000		6,625,000
Joint venture paid																																									1,137,000		1,137,000
Investment by trust																									30,000,000																	3,935,000
Area of collateralized building																																											71,000
Lease expiration date																																											2014-09
Number of Automatic Extensions for building lease																																											6
Extension period for lease																																											5 years
Loan held by this venture																							40,000,000
Acquisition of loan																					32,500,000
Discount accretion income				37,000	14,065,000																7,500,000
Equity income Distribution				19,354,000	17,097,000																13,333,000
Equity income recorded																					2,676,000
Nominal % Ownership																					33.33%				50.00%	50.00%
Loans Receivable		108,163,000		108,163,000		211,250,000																						56,150,000
Aggregate principal payments		5,571,000		30,648,000																															5,571,000	30,648,000
Pay downs of recourse debt														23,770,000	23,770,000
Principal amount of the loan												20,500,000
Office building area, square foot									260,000
LIBOR plus										14.25%
Pari passu participation interest in the loan											50.00%
Loan bears interest, description of variable rate basis				LIBOR plus 3%					0.5% LIBOR floor
Mortgage loan, LIBOR floor rate									0.50%
Interest rate										8.25%
Origination Fee (Amount)												205,000
Proceeds from sale of participation interest in loan								10,250,000
Credit allowed to borrower											100,000
Maturity date of loan							Aug. 01, 2024		Jan. 23, 2015																														May 01, 2016
Gain or loss recognized on the sale of the interest										0
Loan bears interest, description of variable rate basis																																							LIBOR plus 2.0%
Mortgage loan, LIBOR rate																																							0.50%
Loan proceeds received																																							38,472,000
Interest rate on mortgage loan							3.50%																														12.90%
Mortgage loans on real estate reduced investment amount																																						21,098,000
Mortgage loans on real estate effective interest rate on investment																																					19.60%
Net proceeds							4,922,000
Public Offering				2,750,000
Price Of common Share		$ 11.45		$ 11.45
Net Proceeds After Origination Fees Interest Reserve And Closing Expense				$ 30,250,000
Underwriters common shares public offering				412,500