Reportable Segments - Summary of Revenues from Operating Properties, Loan Assets and REIT Securities and Expenses Incurred by Each Segment (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Segment Reporting Information [Line Items]
Net income from segments before corporate income (expense)	$ 7,250,000	$ 6,295,000	$ 7,847,000	$ 20,765,000
Rents and reimbursements	20,165,000	12,372,000	39,228,000	23,769,000
Interest and dividends	2,752,000	4,307,000	8,249,000	9,627,000
Operating expenses	(7,150,000)	(3,870,000)	(14,581,000)	(7,555,000)
Gain (loss) on sale of securities carried at fair value	0	0	2,000	(102,000)
Real estate taxes	(2,420,000)	(1,213,000)	(4,615,000)	(1,950,000)
Equity in (loss) income of equity investments	4,178,000	4,524,000	10,372,000	12,393,000
Operating income	22,917,000	16,679,000	47,477,000	33,396,000
Depreciation and amortization expense	(6,652,000)	(3,894,000)	(13,883,000)	(7,747,000)
Interest expense	(5,830,000)	(6,143,000)	(11,524,000)	(11,615,000)
General and administrative	(2,144,000)	(1,094,000)	(3,786,000)	(1,936,000)
Related party fees	(2,399,000)	(2,291,000)	(4,774,000)	(4,557,000)
Impairment loss on investments in real estate	0	0	(9,200,000)	0
Loss on extinguishment of debt	(564,000)	0	(564,000)	0
Gain on sale of investments in real estate	6,569,000	6,752,000	10,994,000	9,527,000
Transaction costs	(319,000)	(46,000)	(569,000)	(52,000)
Settlement expense	0	(134,000)	0	(134,000)
Income (loss) from continuing operations before non-controlling interest	210,000	1,050,000	(4,972,000)	10,648,000
Income from discontinued operations	6,772,000	6,695,000	11,151,000	10,048,000
Net loss attributable to non-controlling interest	1,980,000	629,000	3,423,000	1,424,000
Net income attributable to Winthrop Realty Trust	8,962,000	8,374,000	9,602,000	22,120,000
Discount accretion	386,000	761,000	1,591,000	1,477,000
Operating Segments [Member]
Segment Reporting Information [Line Items]
Rents and reimbursements	20,165,000	12,372,000	39,228,000	23,769,000
Operating expenses	(7,150,000)	(3,870,000)	(14,581,000)	(7,555,000)
Real estate taxes	(2,420,000)	(1,213,000)	(4,615,000)	(1,950,000)
Operating income	16,321,000	11,005,000	30,115,000	21,090,000
Depreciation and amortization expense	(6,652,000)	(3,894,000)	(13,883,000)	(7,747,000)
Interest expense	(4,191,000)	(3,669,000)	(7,963,000)	(6,734,000)
Impairment loss on investments in real estate	0	0	(9,200,000)	0
Gain on sale of investments in real estate	8,000	0	8,000	0
Settlement expense	0	(134,000)	0	(134,000)
Operating properties net income (loss)	3,064,000	3,308,000	(3,345,000)	6,475,000
Operating Segments [Member] | Fenway-Wateridge [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	7,000	185,000	14,000	387,000
Equity in (loss) income of equity investments	54,000	47,000	106,000	83,000
Operating Segments [Member] | Vintage Housing Holdings [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	557,000	0	557,000	0
Equity in (loss) income of equity investments	2,059,000	2,696,000	3,679,000	4,617,000
Operating Segments [Member] | WRT-Elad [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	1,273,000	167,000	2,509,000	610,000
Operating Segments [Member] | 701 Seventh Avenue [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	1,939,000	623,000	3,497,000	1,320,000
Operating Segments [Member] | Marc Realty [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	12,000	69,000	7,000	9,000
Impairment loss on equity investment	(2,422,000)	0	(2,422,000)	0
Operating Segments [Member] | Sealy Northwest Atlanta [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(138,000)	(87,000)	(266,000)	(233,000)
Operating Segments [Member] | Mentor Retail [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	17,000	16,000	37,000	33,000
Operating Segments [Member] | Atrium Mall [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(53,000)	0	(56,000)	0
Operating Segments [Member] | Edens Plaza Associates [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(1,000)	0	(1,000)	0
Loan Assets [Member]
Segment Reporting Information [Line Items]
Interest income	2,366,000	3,446,000	6,658,000	7,900,000
Unrealized gain (loss) on loan securities carried at fair value	0	215,000	0	215,000
Operating income	4,190,000	5,415,000	11,531,000	15,546,000
Interest expense		(647,000)	(121,000)	(1,227,000)
General and administrative	(4,000)	(21,000)	(220,000)	(35,000)
Operating properties net income (loss)	4,186,000	4,747,000	11,190,000	14,284,000
Discount accretion	386,000	761,000	1,591,000	1,477,000
Loan Assets [Member] | ROIC Lakeside Eagle [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(8,000)	(2,000)	(19,000)	(15,000)
Loan Assets [Member] | Concord Debt Holdings [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	249,000	36,000	515,000	71,000
Loan Assets [Member] | CDH CDO LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	551,000	0	984,000	150,000
Loan Assets [Member] | Concord Debt Holdings [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(2,000)	15,000	88,000	29,000
Loan Assets [Member] | CDH CDO [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	414,000	427,000	1,247,000	907,000
Loan Assets [Member] | WRT-Stamford LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	232,000	224,000	461,000	445,000
Loan Assets [Member] | SoCal Office Loan Portfolio [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	0	(2,000)	0	(2,000)
Loan Assets [Member] | RE CDO Management LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	2,000	(9,000)	6,000	3,761,000
Loan Assets [Member] | 10 Metrotech [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	0	304,000	0	608,000
REIT Securities [Member]
Segment Reporting Information [Line Items]
Interest and dividends	0	100,000	0	250,000
Gain (loss) on sale of securities carried at fair value	0	0	2,000	(102,000)
Unrealized gain (loss) on loan securities carried at fair value	0	(1,860,000)	0	(142,000)
Operating properties net income (loss)	0	(1,760,000)	2,000	6,000
Reconciliations to GAAP Net Income [Member]
Segment Reporting Information [Line Items]
Interest income	114,000	116,000	199,000	185,000
Interest expense	(1,639,000)	(1,827,000)	(3,440,000)	(3,654,000)
General and administrative	(2,140,000)	(1,073,000)	(3,566,000)	(1,901,000)
Related party fees	(2,399,000)	(2,291,000)	(4,774,000)	(4,557,000)
Loss on extinguishment of debt	(564,000)	0	(564,000)	0
Transaction costs	(319,000)	(46,000)	(569,000)	(52,000)
State and local taxes	(93,000)	(124,000)	(105,000)	(138,000)
Income (loss) from continuing operations before non-controlling interest	$ 210,000	$ 1,050,000	$ (4,972,000)	$ 10,648,000