Income Taxes - Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Deferred tax assets:
Accrued employee benefits	$ 11,409	$ 8,285
Allowances for loss contingencies	3,561	3,518
Deferred compensation	3,071	3,272
Intangible assets		1,361
Inventory valuation	8,036	1,154
Long-term contracts	6,995	7,751
Prepaid and accrued expenses	1,816	1,229
Retirement benefits	4,967	1,398
Tax credit carryforwards	33,118	35,137
Loss carryforwards	36,248	29,097
Other	818	264
Total gross deferred tax assets	110,039	92,466
Valuation allowance	(69,098)	(81,838)
Total deferred tax assets	40,941	10,628
Deferred tax liabilities:
Debt obligation basis difference	(4,582)
Deferred revenue	(12,135)	(2,351)
Intangible assets	(18,592)
Property, plant and equipment	(4,524)	(5,079)
Unremitted foreign earnings	(977)	(823)
Other	(587)	(351)
Total deferred tax liabilities	(41,397)	(8,604)
Net deferred tax asset		$ 2,024
Net deferred tax liabilities	$ (456)