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SUPPLEMENTAL BALANCE SHEET INFORMATION - Activity in the Reserve for Bad Debts (Details) - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Reserve for credit losses:      
Balance at October 1, $ 1,820 $ 9,927 $ 6,217
Provision for credit loss 203 2,203 2,321
(Write-off) recovery of credit loss 45 (10,310) 1,389
Balance at September 30,  $ 2,068 $ 1,820 $ 9,927