Earnings per Share - Reconciliation of Net Income (Loss) and Number of Common Shares Used in Computations of Basic Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Numerator - Basic and Diluted
Net loss	$ (28,506)	$ (101,227)	$ (50,708)	$ (120,212)
Preferred dividends	(1,225)	(1,225)	(2,450)	(2,450)
Net loss attributable to Seritage common shareholders	(29,731)	(102,452)	(53,158)	(122,662)
Net loss attributable to Seritage common shareholders - Diluted	$ (29,731)	$ (102,452)	$ (53,158)	$ (122,662)
Denominator - Basic and Diluted
Weighted average Class A common shares outstanding	56,324	56,268	56,304	56,242
Weighted average Class A common shares outstanding - Diluted	56,324	56,268	56,304	56,242
Loss per share attributable to Class A common shareholders - Basic	$ (0.53)	$ (1.82)	$ (0.94)	$ (2.18)
Loss per share attributable to Class A common shareholders - Diluted	$ (0.53)	$ (1.82)	$ (0.94)	$ (2.18)
Class A Common Shares [Member]
Denominator - Basic and Diluted
Weighted average Class A common shares outstanding	56,324	56,268	56,304	56,242