Employee Benefit Plans Change in Projected Benefit Obligation and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Change in projected benefit obligation
Service cost	$ 1,125	$ 898	$ 933
Interest cost	492	699	742
Pension Plan [Member] | Foreign Plan [Member]
Change in projected benefit obligation
Projected benefit obligation at prior year measurement date	42,948	35,541
Service cost	1,125	898
Interest cost	492	699
Actuarial losses	5	8,056
Benefits paid from company assets	(173)	(139)
Plan amendment	0	113
Foreign currency exchange impact	2,992	(2,220)
Projected benefit obligation at measurement date	47,389	42,948	35,541
Change in plan assets
Fair value of assets at prior year measurement date	25,525	24,583
Actual return on plan assets	205	2,269
Benefits paid	(60)	(48)
Employer contribution	255	175
Foreign currency exchange impact	1,605	(1,454)
Fair value of assets at measurement date	27,530	25,525	$ 24,583
Funded status and amount recognized in assets and liabilities	(19,859)	(17,423)
Amount recognized in assets and liabilities
Other non‑current assets	2,831	2,655
Other non‑current liabilities	(22,690)	(20,078)
Amount recognized in accumulated other comprehensive loss, before taxes
Actuarial loss	$ 11,235	$ 11,251