Pension Plans - Change in Benefit Obligation And Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Plan assets at fair value, beginning of year	$ 72,063
Actual return on plan assets	7,400	$ (3,000)	$ 3,500
Employer contributions	3,000	2,600	2,600
Plan assets at fair value—end of year	78,385	72,063
Unrecognized actuarial loss	(30,200)	(37,200)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation, beginning of year	97,832	94,983
Service cost	1,127	1,426	1,372
Interest cost	692	527	1,199
Actuarial loss (gain)	1,100	(2,835)
Foreign exchange impact	(1,562)	6,452
Participant contributions	109	86
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefits paid	(2,786)	(2,234)
Curtailments	0	(573)
Projected benefit obligation, end of year	96,512	97,832	94,983
Plan assets at fair value, beginning of year	72,063	69,879
Actual return on plan assets	7,383	(2,990)
Employer contributions	3,049	2,622
Participant contributions	109	86
Foreign exchange impact	(1,433)	4,700
Benefits paid	(2,786)	(2,234)
Plan assets at fair value—end of year	78,385	72,063	$ 69,879
Underfunded status	(18,127)	(25,769)
Accumulated benefit obligation, end of year	95,090	96,270
Non-current asset	855	0
Non-current liability	(18,615)	(25,437)
Liability, Defined Benefit Plan, Current	(367)	(332)
Unrecognized actuarial loss	$ 30,213	$ 37,175