Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Assets:
Cash and cash equivalents	$ 134,016	$ 160,216
Short-term investments	15,694	18,075
Other assets	8,098	7,351
Liabilities:
Deferred compensation	8,070	6,569
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	134,016	160,216
Short-term investments	15,694	18,075
Other assets	0	0
Liabilities:
Deferred compensation	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents	0	0
Short-term investments	0	0
Other assets	8,098	7,351
Liabilities:
Deferred compensation	8,070	6,569
Significant Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Short-term investments	0	0
Other assets	0	0
Liabilities:
Deferred compensation	$ 0	$ 0