Non-controlling Interests - Schedule of Changes in Trust's Ownership Interest in Subsidiaries (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
Equity [Abstract]
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
Increase (decrease) in Winthrop Realty Trust paid in capital adjustments from transaction with non-controlling interests										103	(4,533)
Changes from net income attributable to Winthrop Realty Trust and transfers (to) from non-controlling interest								$ 12,481		$ 28,881	$ 20,098