Reportable Segments - Summary of Revenues from Operating Properties, Loan Assets and REIT Securities and Expenses Incurred by Each Segment (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Rents and reimbursements	$ 15,099,000	$ 12,224,000	$ 45,026,000	$ 35,022,000
Interest and dividends	3,917,000	3,722,000	13,545,000	15,018,000
Depreciation and amortization expense	(4,923,000)	(4,416,000)	(14,703,000)	(11,623,000)
Gain (loss) on sale of securities carried at fair value	(31,000)		(133,000)	41,000
Real estate taxes	(1,705,000)	(1,160,000)	(4,184,000)	(3,116,000)
Equity in (loss) income of equity investments	13,856,000	12,809,000	26,249,000	14,051,000
Interest income	101,000	242,000	286,000	433,000
Loan discount accretion	806,000	425,000	2,283,000	5,984,000
Interest expense	(5,435,000)	(4,416,000)	(18,175,000)	(11,560,000)
Settlement expense	(16,000)		(150,000)
Loan assets operating income	19,016,000	15,946,000	58,571,000	50,040,000
General and administrative expense	(1,113,000)	(782,000)	(3,058,000)	(2,447,000)
Related party fees	(2,309,000)	(2,316,000)	(6,866,000)	(6,641,000)
Operating properties net income (loss)	12,671,000	8,640,000	37,520,000	21,886,000
Income from continuing operations	12,167,000	15,962,000	23,404,000	25,690,000
(Loss) income from discontinued operations attributable to Winthrop Realty Trust	(1,434,000)	85,000	8,025,000	594,000
Net income	10,733,000	16,047,000	31,429,000	26,284,000
Net loss (income) attributable to non-controlling interest	995,000	(939,000)	2,419,000	435,000
Operating Segments [Member]
Segment Reporting Information [Line Items]
Rents and reimbursements	15,099,000	12,224,000	45,026,000	35,022,000
Depreciation and amortization expense	(4,923,000)	(4,416,000)	(14,703,000)	(11,623,000)
Operating expenses	(5,272,000)	(3,335,000)	(14,697,000)	(10,643,000)
Real estate taxes	(1,705,000)	(1,160,000)	(4,184,000)	(3,116,000)
Interest expense	(3,272,000)	(3,126,000)	(11,131,000)	(9,230,000)
Operating properties net income (loss)	4,460,000	1,098,000	11,536,000	1,033,000
Operating Segments [Member] | Fenway-Wateridge [Member]
Segment Reporting Information [Line Items]
Equity in earnings of preferred equity investment	189,000		576,000
Equity in (loss) income of equity investments	50,000		133,000
Operating Segments [Member] | Sealy Northwest Atlanta [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(130,000)	(109,000)	(363,000)	(273,000)
Operating Segments [Member] | Sealy Newmarket [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments		(704,000)		(2,171,000)
Operating Segments [Member] | Marc Realty [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(26,000)	377,000	(17,000)	33,000
Operating Segments [Member] | WRT Elad [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	905,000	(57,000)	1,515,000	458,000
Operating Segments [Member] | Vintage [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	2,525,000	1,392,000	7,142,000	2,326,000
Operating Segments [Member] | 701 Seventh Avenue [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	1,055,000		2,375,000
Operating Segments [Member] | Mentor [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	12,000	12,000	45,000	18,000
Operating Segments [Member] | Atrium Mall LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(31,000)		(31,000)
Operating Segments [Member] | F-II Co Invest Llc [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments				232,000
Loan Assets [Member]
Segment Reporting Information [Line Items]
Interest income	3,011,000	2,985,000	10,912,000	8,130,000
Loan discount accretion	806,000	425,000	2,283,000	5,984,000
Interest expense	(335,000)	(336,000)	(1,562,000)	(1,004,000)
Unrealized (loss) gain on securities carried at fair value		371,000	215,000	447,000
Loan assets operating income	13,313,000	15,679,000	28,860,000	27,989,000
General and administrative expense	(2,000)	(15,000)	(37,000)	(40,000)
Operating properties net income (loss)	12,976,000	15,328,000	27,261,000	26,945,000
Loan Assets [Member] | Sealy ROIC Riverside [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments		238,000		706,000
Loan Assets [Member] | ROIC Lakeside Eagle [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(7,000)	(16,000)	(22,000)	(32,000)
Loan Assets [Member] | Concord Debt Holdings [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	2,970,000	35,000	3,041,000	386,000
Loan Assets [Member] | CDH CDO LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	265,000	136,000	415,000	670,000
Loan Assets [Member] | Concord Debt Holdings (1) [Member]
Segment Reporting Information [Line Items]
Equity in earnings of preferred equity investment	20,000	2,000	49,000	30,000
Loan Assets [Member] | CDH CDO (1) [Member]
Segment Reporting Information [Line Items]
Equity in earnings of preferred equity investment	3,367,000	855,000	4,274,000	1,333,000
Loan Assets [Member] | WRT-Stamford LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	256,000	232,000	701,000	548,000
Loan Assets [Member] | Socal Office Portfolio Loan LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments		10,348,000	(2,000)	9,710,000
Loan Assets [Member] | RE CDO Management LLC [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	(51,000)	18,000	3,710,000	46,000
Loan Assets [Member] | 10 Metrotech [Member]
Segment Reporting Information [Line Items]
Equity in (loss) income of equity investments	2,676,000	50,000	3,284,000	31,000
REIT Securities [Member]
Segment Reporting Information [Line Items]
Interest and dividends	100,000	312,000	350,000	904,000
Gain (loss) on sale of securities carried at fair value	(31,000)		(133,000)	41,000
Unrealized (loss) gain on securities carried at fair value		3,113,000	(142,000)	7,254,000
Operating properties net income (loss)	69,000	3,425,000	75,000	8,199,000
Net Income Attributable to Winthrop Realty Trust	17,505,000	19,851,000	38,872,000	36,177,000
Reconciliations to GAAP Net Income [Member]
Segment Reporting Information [Line Items]
Interest income	101,000	242,000	286,000	433,000
Interest expense	(1,828,000)	(954,000)	(5,482,000)	(1,326,000)
General and administrative expense	(1,111,000)	(767,000)	(3,021,000)	(2,407,000)
Related party fees	(2,309,000)	(2,316,000)	(6,866,000)	(6,641,000)
Transaction costs	(106,000)	(30,000)	(158,000)	(335,000)
State and local taxes	(85,000)	(64,000)	(227,000)	(211,000)
Income from continuing operations	12,167,000	15,962,000	23,404,000	25,690,000
(Loss) income from discontinued operations attributable to Winthrop Realty Trust	(1,434,000)	85,000	8,025,000	594,000
Net income	10,733,000	16,047,000	31,429,000	26,284,000
Net loss (income) attributable to non-controlling interest	995,000	(939,000)	2,419,000	435,000
Net Income Attributable to Winthrop Realty Trust	$ 11,728,000	$ 15,108,000	$ 33,848,000	$ 26,719,000