Acquisition and Disposition Activity - Additional Information (Detail) (USD $)	3 Months Ended				0 Months Ended	3 Months Ended	0 Months Ended			3 Months Ended	0 Months Ended			0 Months Ended		1 Months Ended	3 Months Ended			0 Months Ended	1 Months Ended	3 Months Ended		0 Months Ended
	Mar. 31, 2014 Investment	Mar. 31, 2013	Feb. 07, 2014	Dec. 31, 2013	Mar. 05, 2014 Norridge [Member]	Mar. 31, 2014 EDITION Hotel [Member] sqft Room	Jan. 10, 2014 Playa Vista Mezzanine Loan [Member]	Feb. 07, 2014 Legacy Orchard Loan [Member]	Feb. 07, 2014 Hotel Wales Loan [Member]	Mar. 31, 2014 Queensridge [Member]	Mar. 05, 2014 Marc Realty [Member]	Mar. 31, 2014 Marc Realty [Member] Minimum [Member]	Mar. 31, 2014 Marc Realty [Member] Maximum [Member]	Mar. 05, 2014 Marc Realty [Member] First Anniversary [Member]	Mar. 05, 2014 Marc Realty [Member] Second Anniversary [Member]	Jan. 31, 2014 701 Seventh Avenue [Member] sqft	Mar. 31, 2014 701 Seventh Avenue [Member] Agreement Room	Mar. 31, 2014 701 Seventh Avenue [Member] Mortgage Loan [Member]	Mar. 31, 2014 701 Seventh Avenue [Member] Mezzanine Loan [Member]	Mar. 05, 2014 Norridge [Member]	Mar. 31, 2014 Norridge [Member]	Mar. 31, 2014 Norridge [Member]	Mar. 05, 2014 Edens [Member]	Feb. 26, 2014 Newbury Apartments Property [Member]
Business Acquisition [Line Items]
Acquisition of issued and outstanding equities																				$ 250,000			$ 250,000
Percentage of ownership interest																				0.375%
Non-controlling interest recorded	16,391,000																			16,391,000		16,391,000
Net income attributable to Winthrop Realty Trust	641,000	13,746,000																			69,000
Revenue	25,004,000	17,374,000																			693,000
Additional capital contributions																	38,723,000
Capital contributions																	92,159,000
Mortgage loan																237,500,000
Mezzanine loan																315,000,000
Area of collateralized building																80,000
Land description																Mezzanine loan to be advanced for construction costs of the approximately 80,000 square feet of retail space which will include an approximately 120 foot high, 20,000 square foot state of the art LED sign.
Loan bears interest, description of variable rate basis	LIBOR plus 3%																LIBOR plus 8%
LIBOR plus																	8.00%
Maturity date of loan																	Jan. 31, 2017
Number of Automatic Extensions for building lease																	2
Extensions period for lease																		2 years	1 year
Supplemental loans amount																	262,500,000
Number rooms in hotel						452											452
Maximum aggregate debt																	815,000,000
Office building area, square foot						30,000
Proceeds from sale of interest in real estate property	5,324,000	11,425,000																						27,500,000
Net proceeds																								5,106,000
Gain or loss on sale of property																								4,422,000
Gross proceeds from sale											6,000,000
Gross proceeds from sale, cash received											1,500,000
Gross proceeds from sale, note receivable	2,506,000			2,229,000							4,500,000
Interest rate, loan bears							16.25%				6.00%			7.00%	8.00%
Note interest maturity, date	Aug. 15, 2022										Mar. 01, 2017
Gain on sale of interest	3,000
Gain on sale of equity investments	69,000
Number of equity investments	3
Aggregate purchase price												5,800,000	6,600,000
Mortgage loan on real estate, increase in principal balance							4,000,000
Mortgage loan on real estate, increase in interest rate							1.50%
Mortgage loan on real estate, share in increased loan amount							2,000,000
Share funded amount							1,992,000
Loan secured by limited partnership interests, face amount					15,500,000
Loan secured by limited partnership interests, basis spread on variable rate					12.00%
Loan secured by limited partnership interests, increase in basis spread on variable rate in each extended term					1.00%
Loan secured by limited partnership interests, stated current interest rate					10.00%
Loan secured by limited partnership interests, annual increase in stated current interest rate					0.50%
Loan secured by limited partnership interests, term					3 years
Description of trusts participation interest in loan					Upon satisfaction of the loan, the Trust will be entitled to a participation interest equal to the greater of (i) a 14.5% internal rate of return ("IRR") (increasing to 15.5% IRR after the initial term) and (ii) 30% (increasing to 40% after the initial term and 50% after the first extended term) of the value of the properties in excess of $115,000,000
Loan participation interest IRR percentage					14.50%
Loan participation interest IRR percentage after initial term					15.50%
Loan participation interest percentage					30.00%
Loan participation interest percentage after initial term					40.00%
Loan participation interest percentage after extended term					50.00%
Minimum value of properties for entitlement to loan participation interest					115,000,000
Sales of interest			42,900,000
Sale price net amount			29,150,000
Retained interest								2.50%	0.50%
Aggregate principle payments										2,908,000
Trust received, exit fee										$ 1,787,000