Income Taxes - Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Deferred tax assets:
Accrued employee benefits	$ 8,285	$ 15,863
Long-term contracts and inventory valuation reductions	8,238	13,974
Allowances for loss contingencies	3,232	4,212
Deferred compensation	3,272	4,830
Intangible assets	1,361
Retirement benefits	1,398	6,214
Tax credit carryforwards	35,137	31,161
Net operating losses carryforwards	29,097	3,715
Other	2,173	2,762
Total gross deferred tax assets	92,193	82,731
Valuation allowance	(81,839)	(57,106)
Total deferred tax assets	10,354	25,625
Deferred tax liabilities:
Deferred revenue	(2,351)	(3,729)
Unremitted foreign earnings	(687)	(11,910)
Property, plant and equipment	(5,079)	(3,137)
Intangible assets		(9,713)
Other	(213)	(158)
Total deferred tax liabilities	(8,330)	(28,647)
Net deferred tax asset	$ 2,024
Net deferred tax liabilities		$ (3,022)