Income Taxes - Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Sep. 30, 2016
Deferred tax assets:
Accrued employee benefits	$ 18,747	$ 15,133
Long-term contracts and inventory valuation reductions	14,490	12,697
Allowances for loss contingencies	6,038	5,754
Deferred compensation	4,830	4,369
Retirement benefits	6,214	12,282
Tax credit carryforwards	31,161	16,512
Net operating losses carryforwards	3,968	12,713
Other	2,652	2,796
Total gross deferred tax assets	88,100	82,256
Valuation allowance	(58,837)	(47,887)
Total deferred tax assets	29,263	34,369
Deferred tax liabilities:
Deferred revenue	(15,085)	(19,952)
Unremitted foreign earnings	(11,910)	(2,347)
Property, plant and equipment	(2,081)	(33)
Intangible assets	(8,176)	(12,894)
Foreign currency mark-to-market		(191)
Other	(212)	(740)
Total deferred tax liabilities	(37,464)	(36,157)
Net deferred tax liabilities	$ (8,201)	$ (1,788)