Income Taxes - Deferred tax assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Deferred tax assets attributable to:
Foreign loss carryforwards	$ 30,548	$ 34,007
Accrued liabilities	24,023	18,662
Share-based compensation expense	7,320	8,392
U.S. foreign tax credits	10,712	11,199
U.S. federal social security tax deferral		3,089
Inventory adjustments	8,156	2,754
Other	(391)	2,984
Total deferred tax assets	80,368	81,087
Valuation allowance	(31,920)	(51,810)
Total deferred tax assets, net	48,448	29,277
Deferred tax liabilities attributable to:
Depreciation and amortization	112,115	109,038
Net deferred tax liability	63,667	79,761
Valuation allowances reduced	(19,900)
Domestic earnings before provision for income taxes	205,200	288,000	$ 168,000
Foreign earnings before provision for income (loss) taxes	38,900	36,900	$ (8,000)
Total operating loss carry-forward	110,800	125,700
Operating loss carry-forward, subject to valuation allowance	60,900	109,400
Amount of operating loss carry-forwards with an expiration date	5,600
Amount of operating loss carry-forwards without an expiration date	105,200
Total tax credit carryforwards	13,100	14,100
Expiring tax credit carryforwards	800
Expiring tax credit carryforwards	400
Non-expiring tax credit carryforwards	1,200
Total Tax credit carryforwards, subject to a valuation allowance	11,900	$ 12,600
U.S. foreign
Deferred tax liabilities attributable to:
Expiring tax credit carryforwards	$ 10,700