Federal and State Income Taxes - Summary of GAAP Net Income Attributable to Trust to Taxable Income (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
Income Tax Disclosure [Abstract]
Net income (loss) 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
Book/Tax differences from depreciation and amortization expense									(2,626)	9,563	5,297
Book/Tax differences of accretion of discount									(3,407)	(4,121)	(8,333)
Book/Tax differences of unrealized gains									766	(73)	(6,923)
Book/Tax differences on gains/losses from capital transactions									11,053	(14,848)	(1,876)
Book/Tax differences on Preferred Shares									0	0	0
Book/Tax differences for impairment losses									9,399	2,904	3,260
Book/Tax differences on investments in unconsolidated joint ventures									(15,611)	(17,880)	4,131
Other book/tax differences, net									(13,918)	4,194	(8,781)
Book/Tax differences on dividend income											(452)
Book/Tax differences of market discount									9,615		14,065
Book/Tax difference due to liquidation accounting									33,812
Taxable income									$ 41,564	$ 8,517	$ 25,019