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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator
Net loss (income)	$ (25,885)	$ (10,602)	$ (36,779)	$ 5,599
Net income (loss) attributable to non-controlling interests	8,982	3,831	12,909	(2,042)
Preferred dividends	(1,225)	(1,225)	(2,450)	(2,453)
Net (loss) income attributable to Seritage common shareholders	(18,128)	(7,996)	(26,320)	1,104
Earnings allocated to unvested participating securities				(4)
Net income (loss) available to common shareholders - Basic and diluted	$ (18,128)	$ (7,996)	$ (26,320)	$ 1,100
Denominator
Weighted average Class A and Class C common shares outstanding - Basic	36,291	35,483	35,983	35,449
Restricted shares and share units				139
Weighted average Class A and Class C common shares outstanding - Diluted	36,291	35,483	35,983	35,588
Net income (loss) per share attributable to Class A and Class C common shareholders - Basic	$ (0.50)	$ (0.23)	$ (0.73)	$ 0.03
Net income (loss) per share attributable to Class A and Class C common shareholders - Diluted	$ (0.50)	$ (0.23)	$ (0.73)	$ 0.03
Class A Common Shares [Member]
Denominator
Weighted average Class A and Class C common shares outstanding - Basic	36,291	35,372	35,983	34,527
Class C Common Shares [Member]
Denominator
Weighted average Class A and Class C common shares outstanding - Basic		111		922