Acquisition and Disposition Activities - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended						7 Months Ended	12 Months Ended			0 Months Ended									1 Months Ended	0 Months Ended				5 Months Ended
	Dec. 09, 2014	Jul. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Jul. 31, 2014	Dec. 31, 2014 Investment Room	Dec. 31, 2013	Dec. 31, 2012	Oct. 15, 2014	Oct. 01, 2014	Oct. 16, 2014	Oct. 20, 2014	Oct. 24, 2014	Nov. 25, 2014	Dec. 02, 2014	Dec. 23, 2014	Jun. 25, 2014	Jun. 30, 2014	May 01, 2014	Aug. 01, 2014	Mar. 05, 2014	Feb. 26, 2014	Jul. 31, 2014	Aug. 06, 2014	Jan. 31, 2014 sqft
Business Acquisition [Line Items]
Non-controlling interest recorded									$ 16,391,000
Net loss attributable to Winthrop Realty Trust		2,879,000	8,962,000	641,000	(5,070,000)	11,728,000	8,374,000	13,746,000	12,481,000	12,481,000	28,778,000	24,631,000
Revenue		8,479,000	22,917,000	24,560,000	21,330,000	15,844,000	16,579,000	16,567,000	55,956,000		70,320,000	55,053,000
Loan bears interest, description of variable rate basis										LIBOR plus 3%
Number of hotel rooms										452
Proceeds from sale of interest in real estate property									56,423,000		38,690,000	7,024,000
Net proceeds	33,959,000
Gross proceeds from sale, note receivable					2,229,000						2,229,000
Note interest maturity date										Aug. 15, 2022
Gain on sale of interest										3,000
Gain on sale of equity investments										69,000
Number of equity investments										3
Payment of loan											23,770,000	1,230,000
5400 Westheimer [Member]
Business Acquisition [Line Items]
Liquidation value of investment																								10,777,000
Net proceeds from loan repayment														1,033,000
Proceeds from sale of interest in joint venture													9,690,000
Waterford [Member]
Business Acquisition [Line Items]
Gross proceeds from sale															15,290,000
Net proceeds from sale of real estate property															28,160,000
Liquidation value of property																								28,160,000
Kroger Atlanta [Member]
Business Acquisition [Line Items]
Gross proceeds from sale																1,464,000
Net proceeds from sale of real estate property																1,500,000
Liquidation value of property																								2,000,000
Kroger Greensboro [Member]
Business Acquisition [Line Items]
Gross proceeds from sale																1,709,000
Liquidation value of investment																								2,500,000
Net proceeds from sale of real estate property																1,750,000
San Pedro [Member]
Business Acquisition [Line Items]
Loan bears interest, description of variable rate basis										-
Gross proceeds from sale																	23,090,000
Net proceeds from sale of real estate property																	23,800,000
Liquidation value of property																								23,800,000
Ownership percentage in real estate investment																	83.70%
Number of properties																	4
Kroger Louisville [Member]
Business Acquisition [Line Items]
Gross proceeds from sale																		2,334,000
Net proceeds from sale of real estate property																		2,500,000
Liquidation value of property																								2,500,000
1515 Market Street Loan Modification [Member]
Business Acquisition [Line Items]
Gross proceeds from sale																			40,304,000
Net proceeds from sale of real estate property																			82,345,000
Liquidation value of property																								81,314,000
Burlington [Member]
Business Acquisition [Line Items]
Gross proceeds from sale																				2,475,000
Net proceeds from sale of real estate property																				2,850,000
Liquidation value of property																								3,225,000
Sealy Northwest Atlanta [Member]
Business Acquisition [Line Items]
Gross proceeds from sale																				5,641,000
Liquidation value of property																								5,692,000
Amherst [Member]
Business Acquisition [Line Items]
Proceeds from sale of interest in real estate property																					24,500,000
Net proceeds																					21,226,000
Gain or loss on sale of property																					946,000	946,000
Revenue from reserve holdback																					2,449,000
Net proceeds from sale of real estate property																					23,675,000	24,500,000
Fenway-Wateridge [Member]
Business Acquisition [Line Items]
Liquidation value of investment																												2,383,000
Crossroads [Member]
Business Acquisition [Line Items]
Net proceeds																							29,633,000
Gain or loss on sale of property																							5,723,000
Gross proceeds from sale																							31,100,000
Marc Realty [Member]
Business Acquisition [Line Items]
Gross proceeds from sale																								5,770,000	6,000,000
Gross proceeds from sale, cash received																									1,500,000
Gross proceeds from sale, note receivable																									4,500,000
Interest rate of loan																									6.00%
Note interest maturity date										Mar. 01, 2017
Liquidation value of investment																								5,770,000
Marc Realty [Member] | First Anniversary [Member]
Business Acquisition [Line Items]
Interest rate of loan																									7.00%
Marc Realty [Member] | Second Anniversary [Member]
Business Acquisition [Line Items]
Interest rate of loan																									8.00%
EDITION Hotel [Member]
Business Acquisition [Line Items]
Office building area, square feet										30,000
Newbury Apartments Property [Member]
Business Acquisition [Line Items]
Proceeds from sale of interest in real estate property																										27,500,000
Net proceeds																										5,106,000
Gain or loss on sale of property																										4,422,000
Apartment Building [Member] | San Pedro [Member]
Business Acquisition [Line Items]
Payment of loan																	150,000,000
Norridge [Member]
Business Acquisition [Line Items]
Acquisition of issued and outstanding equities																									250,000
Percentage of ownership interest																									0.375%
Non-controlling interest recorded																									16,391,000
Net loss attributable to Winthrop Realty Trust																											2,000
Revenue																											2,862,000
Edens Properties [Member]
Business Acquisition [Line Items]
Acquisition of issued and outstanding equities																									250,000
701 Seventh Avenue [Member]
Business Acquisition [Line Items]
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.
Loan bears interest, description of variable rate basis										LIBOR plus 8%
LIBOR plus										8.00%
Maturity date of loan										Jan. 31, 2017
Number of Automatic Extensions for building lease										2
Supplemental loans										262,500,000
Number of hotel rooms										452
Maximum aggregate debt										$ 815,000,000
701 Seventh Avenue [Member] | Mortgage Loan [Member]
Business Acquisition [Line Items]
Extension period for lease										2 years
701 Seventh Avenue [Member] | Mezzanine Loan [Member]
Business Acquisition [Line Items]
Extension period for lease										1 year