Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Current:
Federal	$ 14,566	$ 1,299	$ 8,071
State	2,180	(423)	2,236
Foreign	12,482	15,371	9,559
Current income tax	29,228	16,247	19,866
Deferred:
Federal	(8,575)	7,003	13,987
State	(957)	947	132
Foreign	893	(249)	(3,535)
Deferred income taxes	(8,639)	7,701	10,584
Total provision	$ 20,589	$ 23,948	$ 30,450