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	9 Months Ended
	Jul. 31, 2014	Sep. 30, 2013	Jul. 31, 2014	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]
Net income from segments before corporate income (expense)	$ 3,993	$ 17,456	$ 11,832		$ 38,222
Rents and reimbursements	7,085	12,026	46,313		35,795
Interest and dividends	1,394	3,917	9,643		13,545
Interest income	37	101	244		286
Operating expenses	(2,546)	(4,302)	(17,127)		(11,856)
Gain (loss) on sale of securities carried at fair value		(31)	2		(133)
Real estate taxes	(764)	(1,172)	(5,379)		(3,122)
Equity in (loss) income of equity investments	2,250	13,856	12,622		26,249
Operating income	8,479	15,943	55,956		49,340
Depreciation and amortization expense	(2,074)	(3,846)	(15,957)		(11,594)
Interest expense	(1,870)	(4,992)	(13,394)		(16,607)
General and administrative	(497)	(1,104)	(4,283)		(3,040)
Related party fees	(774)	(2,309)	(5,548)		(6,866)
Impairment loss on investments in real estate			(9,200)
Loss on extinguishment of debt			(564)
Settlement expense		(16)			(150)
Transaction costs	(17)	(106)	(586)		(158)
Income (loss) from continuing operations	2,400	12,128	(2,572)		22,776
Income (loss) from discontinued operations attributable to Winthrop Realty Trust	84	(1,395)	11,235		8,653
Net loss attributable to non-controlling interests	395	995	3,818		2,419
Net income attributable to Winthrop Realty Trust	2,879	11,728	12,481		33,848
Interest income			247		395
Discount accretion	495	806	2,086	2,086	2,283
Operating Segments [Member]
Segment Reporting Information [Line Items]
Rents and reimbursements	7,085	12,026	46,313		35,795
Operating expenses	(2,546)	(4,301)	(17,127)		(11,856)
Real estate taxes	(764)	(1,172)	(5,379)		(3,122)
Operating income	5,765	11,102	35,880		32,192
Depreciation and amortization expense	(2,074)	(3,847)	(15,957)		(11,594)
Interest expense	(1,360)	(2,829)	(9,323)		(9,563)
Impairment loss on investments in real estate			(9,200)
Settlement expense		(16)			(150)
Operating properties net income (loss)	2,331	4,410	(1,022)		10,885
Operating Segments [Member] | Fenway-Wateridge [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	3	189	17		576
Equity in (loss) income of equity investments	36	50	142		133
Operating Segments [Member] | Vintage Housing Holdings [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	8		565
Equity in (loss) income of equity investments	608	2,525	4,287		7,142
Operating Segments [Member] | WRT-Elad [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	418	905	2,927		1,515
Operating Segments [Member] | 701 Seventh Avenue [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	896	1,055	4,393		2,375
Operating Segments [Member] | Marc Realty [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(26)	(26)	(19)		(17)
Impairment loss on equity investment			(2,422)
Operating Segments [Member] | Sealy Northwest Atlanta [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(22)	(130)	(288)		(363)
Operating Segments [Member] | Mentor Retail [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	6	12	43		45
Operating Segments [Member] | Atrium Mall [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	63	(31)	7		(31)
Operating Segments [Member] | Edens Plaza Associates [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments			(1)
Loan Assets [Member]
Segment Reporting Information [Line Items]
Unrealized gain (loss) on loan securities carried at fair value					215
Operating income	1,665	13,313	13,196		28,860
Interest expense		(335)	(121)		(1,562)
General and administrative	(3)	(1)	(223)		(36)
Operating properties net income (loss)	1,662	12,977	12,852		27,262
Interest income	899	3,011	7,557		10,912
Discount accretion	495	806	2,086		2,283
Loan Assets [Member] | ROIC Lakeside Eagle [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(1)	(7)	(20)		(22)
Loan Assets [Member] | Concord Debt Holdings [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	32	2,970	547		3,041
Loan Assets [Member] | CDH CDO LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	81	265	1,065		415
Loan Assets [Member] | Concord Debt Holdings from Lexington Realty Trust [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(1)	20	87		49
Loan Assets [Member] | CDH CDO [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	79	3,367	1,326		4,274
Loan Assets [Member] | WRT-Stamford LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	80	256	541		701
Loan Assets [Member] | SoCal Office Loan Portfolio [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments					(2)
Loan Assets [Member] | RE CDO Management LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	1	(51)	7		3,710
Loan Assets [Member] | 10 Metrotech [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments		2,676			3,284
REIT Securities [Member]
Segment Reporting Information [Line Items]
Interest and dividends		100			350
Gain (loss) on sale of securities carried at fair value		(31)	2		(133)
Unrealized gain (loss) on loan securities carried at fair value					142
Operating properties net income (loss)		69	2		75
Reconciliations to GAAP Net Income [Member]
Segment Reporting Information [Line Items]
Interest income	37	101	244		286
Interest expense	(510)	(1,828)	(3,950)		(5,482)
General and administrative	(494)	(1,103)	(4,060)		(3,004)
Related party fees	(774)	(2,309)	(5,548)		(6,866)
Loss on extinguishment of debt			(564)
Transaction costs	(17)	(106)	(586)		(158)
Federal, state and local taxes	165	(83)	60		(222)
Income (loss) from continuing operations	$ 2,400	$ 12,128	$ (2,572)		$ 22,776