v3.26.1
(Loss) income per Share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Net (loss) income attributable to Fluence Energy, Inc. - basic $ (32,817) $ 6,252 $ (98,814) $ (66,260)
Net (loss) income attributable to Fluence Energy, Inc. - basic (in shares) 138,129,139 130,723,258 134,060,941 130,062,109
Net (loss) income attributable to Fluence Energy, Inc. - basic (in usd per share) $ (0.24) $ 0.05 $ (0.74) $ (0.51)
Net (loss) income attributable to Fluence Energy, Inc. - diluted $ (32,817) $ 1,986 $ (98,814) $ (66,260)
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in shares) 138,129,139 183,645,493 134,060,941 130,062,109
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in usd per share) $ (0.24) $ 0.01 $ (0.74) $ (0.51)
Class B-1 common stock        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Net (loss) income attributable to Fluence Energy, Inc. - diluted $ 0 $ (4,266)    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in shares) 0 51,499,195    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in usd per share)    
Outstanding pre-IPO options issued pursuant to the 2020 Unit Option Plan        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Net (loss) income attributable to Fluence Energy, Inc. - diluted $ 0 $ 0    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in shares) 0 1,197,408    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in usd per share)    
Outstanding phantom units        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Net (loss) income attributable to Fluence Energy, Inc. - diluted $ 0 $ 0    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in shares) 0 0    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in usd per share)    
Restricted Stock Units (RSUs)        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Net (loss) income attributable to Fluence Energy, Inc. - diluted $ 0 $ 0    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in shares) 0 225,632    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in usd per share)    
Outstanding performance share units (“PSUs”)        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Net (loss) income attributable to Fluence Energy, Inc. - diluted $ 0 $ 0    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in shares) 0 0    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in usd per share)    
Outstanding non-qualified stock options        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Net (loss) income attributable to Fluence Energy, Inc. - diluted $ 0 $ 0    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in shares) 0 0    
Net (loss) income attributable to Fluence Energy, Inc. - diluted (in usd per share)