Acquisition and Disposition Activity - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended	7 Months Ended	9 Months Ended					0 Months Ended	9 Months Ended		0 Months Ended							0 Months Ended		0 Months Ended	9 Months Ended		0 Months Ended			3 Months Ended	0 Months Ended		0 Months Ended		0 Months Ended		5 Months Ended		0 Months Ended	9 Months Ended		9 Months Ended		0 Months Ended		9 Months Ended	0 Months Ended
	Feb. 07, 2014	Jul. 31, 2014	Sep. 30, 2013	Jul. 31, 2014	Sep. 30, 2014 Investment	Sep. 30, 2013	Feb. 07, 2014	Dec. 31, 2013	Sep. 15, 2014 Series D Preferred Shares of Beneficial Interest [Member]	Mar. 05, 2014 Edens Center and Norridge Commons [Member]	Sep. 30, 2014 Edens Center and Norridge Commons [Member]	Mar. 05, 2014 Edens Center and Norridge Commons [Member]	Jul. 07, 2014 Playa Vista Mezzanine Loan [Member]	Jan. 10, 2014 Playa Vista Mezzanine Loan [Member]	Jul. 07, 2014 Playa Vista Mezzanine Loan [Member]	Jan. 10, 2014 Playa Vista Mezzanine Loan [Member]	Feb. 07, 2014 Legacy Orchard Loan [Member]	Feb. 07, 2014 Hotel Wales Loan [Member]	Aug. 06, 2014 Fenway-Wateridge [Member]	Sep. 10, 2014 Notes Payable [Member] KeyBank National Association [Member]	Sep. 10, 2014 Notes Payable [Member] KeyBank National Association [Member] Option	Mar. 05, 2014 Marc Realty [Member]	Sep. 30, 2014 Marc Realty [Member]	Mar. 05, 2014 Marc Realty [Member]	Mar. 05, 2014 Marc Realty [Member] First Anniversary [Member]	Mar. 05, 2014 Marc Realty [Member] Second Anniversary [Member]	May 01, 2014 Crossroads [Member]	Mar. 31, 2014 Queensridge [Member]	Jun. 25, 2014 Amherst [Member]	Sep. 06, 2014 Stamford [Member]	Aug. 07, 2014 The Shops at Wailea [Member]	Aug. 07, 2014 The Shops at Wailea [Member]	Sep. 10, 2014 London Interbank Offered Rate (LIBOR) [Member] Notes Payable [Member] KeyBank National Association [Member]	Mar. 05, 2014 Norridge [Member]	Jul. 31, 2014 Norridge [Member]	Mar. 05, 2014 Norridge [Member]	Mar. 05, 2014 Edens Plaza Associates [Member]	Sep. 30, 2014 701 Seventh Avenue [Member] Agreement Room	Jan. 31, 2014 701 Seventh Avenue [Member] sqft	Sep. 30, 2014 701 Seventh Avenue [Member] Mortgage Loan [Member]	Sep. 30, 2014 701 Seventh Avenue [Member] Mezzanine Loan [Member]	Aug. 06, 2014 Office [Member] Stamford [Member]	Aug. 06, 2014 Office [Member] Stamford [Member] Office	Sep. 30, 2014 EDITION Hotel [Member] sqft Room	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
Net loss attributable to Winthrop Realty Trust		2,879,000	11,728,000	12,481,000		33,848,000																													2,000
Revenue		8,479,000	15,943,000	55,956,000		49,340,000																													2,862,000
Additional capital contributions																																						53,187,000
Capital contributions																																						106,624,000
Mortgage loan																																							237,500,000
Mezzanine loan																																							315,000,000
Area of collateralized building																																							110,000
Land description																																						Mezzanine loan to be advanced for construction costs of the approximately 110,000 square feet of retail space and an approximately 120 foot high, 20,000 square foot state of the art LED sign.
Interest rate, description					LIBOR plus 3%																												LIBOR plus 3%					LIBOR plus 8%
LIBOR plus																																	3.00%					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				56,423,000		36,217,000																							24,500,000																27,500,000
Net proceeds																											29,633,000		21,226,000																5,106,000
Gain or loss on sale of property																											5,723,000		946,000																4,422,000
Gross proceeds from sale																						6,000,000	5,770,000				31,100,000
Gross proceeds from sale, cash received																						1,500,000
Gross proceeds from sale, note receivable								2,229,000																4,500,000
Interest rate, loan bears														16.25%								6.00%			7.00%	8.00%
Debt instrument, maturity date					Aug. 15, 2022															Mar. 10, 2015			Mar. 01, 2017
Gain on sale of interest					3,000
Gain on sale of equity investments					69,000
Number of equity investments					3
Liquidation value of investment																			2,383,000				5,770,000							9,450,000		7,516,000
Revenue from reserve holdback																													2,449,000
Net proceeds from sale of real estate property																													23,675,000
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%
Gain (loss) on sale of loan	0
Aggregate principle payments																												2,908,000
Trust received, exit fee																												1,787,000
Outstanding loans acquired for aggregate price				31,492,000		21,437,000							14,000,000
Ownership percentage															50.00%
Payment of interest accrued				15,280,000		17,780,000							108,000
Premium amount included in purchase price															762,000
Net proceeds from distributions of venture																																										9,450,000
Number of office properties																																											7
Net proceeds from loan repayment																															7,556,000
Line of credit								0													25,000,000
Periodic Interest repayment																				Monthly
Extension options																					2
Period of Extension Options																				3 months
Liquidating distribution									$ 122,821,000
Liquidating distribution per share								$ 25	$ 25.4815