Stock-Based Compensation - Summary of Profits Interest Awards (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2022	Mar. 31, 2022	Sep. 30, 2021
Vested Units
Awards that met performance target, percent	83.00%
Awards failed to meet performance, percent	17.00%
Weber HoldCo LLC Units | Hybrid Units
Vested Units
Aggregate intrinsic value of vested hybrid units (in shares)	$ 0.1	$ 0.1
Profits Interest Plan | Service-Based Units
Nonvested Units
Units Outstanding (in shares)	10,707,266	10,707,266	11,713,015
Weighted Average Exercise Price (in dollars per share)	$ 8.01	$ 8.01	$ 8.13
Weighted Average Fair Value (in dollars per share)	$ 9.10	$ 9.10	$ 8.97
Vested Units
Units Outstanding (in shares)		(1,005,749)
Weighted Average Exercise Price (in dollars per share)		$ 9.43
Weighted Average Fair Value (in dollars per share)		$ 7.59
Aggregate intrinsic value of vested hybrid units (in shares)	$ 28.0	$ 28.0
Profits Interest Plan | Service-Based Units | Vested
Nonvested Units
Units Outstanding (in shares)	5,353,632	5,353,632	4,347,883
Weighted Average Exercise Price (in dollars per share)	$ 8.01	$ 8.01	$ 7.68
Weighted Average Fair Value (in dollars per share)	$ 8.86	$ 8.86	$ 9.15
Vested Units
Units Outstanding (in shares)		1,005,749
Weighted Average Exercise Price (in dollars per share)		$ 9.43
Weighted Average Fair Value (in dollars per share)		$ 7.59
Aggregate intrinsic value of vested hybrid units (in shares)	$ 9.3	$ 9.3
Profits Interest Plan | Hybrid Units
Nonvested Units
Units Outstanding (in shares)	1,185,180	1,185,180	1,777,770
Weighted Average Exercise Price (in dollars per share)	$ 9.54	$ 9.54	$ 9.54
Weighted Average Fair Value (in dollars per share)	$ 8.09	$ 8.09	$ 7.88
Vested Units
Units Outstanding (in shares)		(592,590)
Weighted Average Exercise Price (in dollars per share)		$ 9.54
Weighted Average Fair Value (in dollars per share)		$ 7.48
Aggregate intrinsic value of vested hybrid units (in shares)	$ 0.3	$ 0.3
Profits Interest Plan | Hybrid Units | Vested
Nonvested Units
Units Outstanding (in shares)	491,849	491,849	0
Weighted Average Exercise Price (in dollars per share)	$ 9.54	$ 9.54	$ 0
Weighted Average Fair Value (in dollars per share)	$ 7.48	$ 7.48	$ 0
Vested Units
Units Outstanding (in shares)		592,590
Weighted Average Exercise Price (in dollars per share)		$ 9.54
Weighted Average Fair Value (in dollars per share)		$ 7.48
Units, Adjustment to vested hybrid units (in shares)		(100,741)
Weighted Average Exercise Price, Adjustment to vested hybrid units (in dollars per share)		$ 9.54
Weighted Average Fair Value, Adjustment to vested hybrid units (in dollars per share)		$ 7.48