Reportable Segments - Summary of Revenues from Operating Properties, Loan Assets and REIT Securities and Expenses Incurred by Each Segment (Detail) (USD $) In Thousands, unless otherwise specified	1 Months Ended	3 Months Ended						7 Months Ended	12 Months Ended
	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	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Rents and reimbursements								$ 46,313		$ 51,865	$ 33,930
Interest and dividends								9,643		18,455	21,123
Operating expenses								(17,127)		(17,769)	(10,814)
Discount accretion								2,086	2,086	4,121	8,333
Interest and other income								244		375	699
Gain on sale of securities carried at fair value								2		742	41
Real estate taxes								(5,379)		(4,926)	(2,598)
Realized gain on sale of loan securities carried at fair value											614
Unrealized gain (loss) on securities carried at fair value										(142)	6,916
Equity in (loss) income of equity investments								12,622		22,641	14,843
Operating income	8,479	22,917	24,560	21,330	15,844	16,579	16,567	55,956		70,320	55,053
Depreciation and amortization expense								(15,957)		(17,275)	(11,277)
General and administrative								(4,283)		(4,356)	(3,529)
Related party fees								(5,548)		(9,289)	(8,953)
Transaction costs								(586)		(1,885)	(421)
Interest expense								(13,394)		(22,365)	(15,533)
Impairment loss on investments in real estate								(9,200)			(1,738)
Provision for loss on loans receivable								0		(348)
Impairment loss on equity investments								2,422		7,687	0
Loss on extinguishment of debt								(564)			(121)
Settlement expense										(411)
Income (loss) from continuing operations								(2,572)		15,716	23,399
Income from discontinued operations attributable to Winthrop Realty Trust								11,235		8,772	985
Non-controlling interest								3,818		4,290	247
Net income attributable to Winthrop Realty Trust	2,879	8,962	641	(5,070)	11,728	8,374	13,746	12,481	12,481	28,778	24,631
RE CDO Management LLC [Member]
Segment Reporting Information [Line Items]
Operating income									149	226	618
General and administrative									(79)	(290)	(354)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net income from segments before corporate income (expense)								11,832		38,561	38,865
Operating Segments [Member] | Operating Properties [Member]
Segment Reporting Information [Line Items]
Rents and reimbursements								46,313		51,865	33,930
Operating expenses								(17,127)		(17,769)	(10,814)
Real estate taxes								(5,379)		(4,926)	(2,598)
Operating income								35,880		43,120	23,136
Depreciation and amortization expense								(15,957)		(17,275)	(11,277)
Interest expense								(9,323)		(13,157)	(10,886)
Impairment loss on investments in real estate								(9,200)			(1,738)
Loss on extinguishment of debt											(121)
Settlement expense										(411)
Operating properties net income (loss)								(1,022)		4,590	(886)
Operating Segments [Member] | Operating Properties [Member] | Fenway-Wateridge [Member]
Segment Reporting Information [Line Items]
Equity in earnings of preferred equity investment								17		613
Equity in (loss) income of equity investments								142		183
Operating Segments [Member] | Operating Properties [Member] | Vintage Housing Holdings [Member]
Segment Reporting Information [Line Items]
Equity in earnings of preferred equity investment								565
Equity in (loss) income of equity investments								4,287		9,174	4,603
Operating Segments [Member] | Operating Properties [Member] | Marc Realty [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								(19)		(284)	33
Impairment loss on equity investments								(2,422)		(7,687)
Operating Segments [Member] | Operating Properties [Member] | Sealy Northwest Atlanta [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								(288)		(469)	(388)
Operating Segments [Member] | Operating Properties [Member] | Sealy Newmarket [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments											(2,811)
Operating Segments [Member] | Operating Properties [Member] | WRT-Elad [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								2,927		1,315	903
Operating Segments [Member] | Operating Properties [Member] | Mentor Retail [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								43		84	46
Operating Segments [Member] | Operating Properties [Member] | 701 Seventh Avenue [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								4,393		3,424
Operating Segments [Member] | Operating Properties [Member] | Atrium Mall [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								7		(90)
Operating Segments [Member] | Operating Properties [Member] | F-II Co Invest LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments											232
Operating Segments [Member] | Operating Properties [Member] | Edens Properties [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								(1)
Operating Segments [Member] | Loan Assets [Member]
Segment Reporting Information [Line Items]
Interest income								7,557		14,334	11,736
Discount accretion								2,086		4,121	8,333
Realized gain on sale of loan securities carried at fair value											614
Unrealized gain on loan securities carried at fair value										215	447
Operating income								13,196		35,661	33,355
General and administrative								(223)		(44)	(121)
Interest expense								(121)		(1,898)	(1,494)
Provision for loss on loans receivable										(348)
Operating properties net income (loss)								12,852		33,371	31,740
Operating Segments [Member] | Loan Assets [Member] | Concord Debt Holdings [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								547		3,072	422
Operating Segments [Member] | Loan Assets [Member] | CDH CDO LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								1,065		1,033	1,715
Operating Segments [Member] | Loan Assets [Member] | Concord Debt Holdings from Lexington Realty Trust [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								87		64	(456)
Operating Segments [Member] | Loan Assets [Member] | CDH CDO [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								1,326		4,926	(997)
Operating Segments [Member] | Loan Assets [Member] | Sealy ROIC Riverside [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments											706
Operating Segments [Member] | Loan Assets [Member] | ROIC Lakeside Eagle [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								(20)		(25)	(42)
Operating Segments [Member] | Loan Assets [Member] | RE CDO Management LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								7		3,709	67
Operating Segments [Member] | Loan Assets [Member] | SoCal Office Loan Portfolio [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments										(2)	9,706
Operating Segments [Member] | Loan Assets [Member] | WRT-Stamford LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments								541		930	769
Operating Segments [Member] | Loan Assets [Member] | 10 Metrotech [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments										3,284	335
Operating Segments [Member] | REIT Securities [Member]
Segment Reporting Information [Line Items]
Interest and dividends											1,054
Gain on sale of securities carried at fair value								2		742	41
Unrealized gain (loss) on securities carried at fair value										(142)	6,916
Operating properties net income (loss)								2		600	8,011
Reconciliations to GAAP Net Income [Member]
Segment Reporting Information [Line Items]
Interest and other income								244		375	699
General and administrative								(4,060)		(4,312)	(3,408)
Related party fees								(5,548)		(9,289)	(8,953)
Transaction costs								(586)		(1,885)	(421)
Interest expense								(3,950)		(7,310)	(3,153)
Loss on extinguishment of debt								(564)
Federal, state and local taxes								$ 60		$ (424)	$ (230)