INCOME TAXES - Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2016
Deferred tax assets:
Accrued employee benefits	$ 12,597	$ 15,133
Long-term contracts and inventory valuation reductions	13,297	12,697
Allowances for loss contingencies	3,793	5,754
Deferred compensation	4,252	4,369
Property, plant and equipment	1,611
Intangible assets	8,037
Retirement benefits	8,040	12,282
Tax credit carryforwards	11,151	16,512
Net operating losses carryforwards	14,795	12,713
Other	1,380	2,796
Total gross deferred tax assets	78,953	82,256
Valuation allowance	(54,759)	(47,887)
Total deferred tax assets	24,194	34,369
Deferred tax liabilities:
Deferred revenue	(23,981)	(19,952)
Unremitted foreign earnings	(535)	(2,347)
Property, plant and equipment		(33)
Intangible assets		(12,894)
Foreign currency mark-to-market		(191)
Other	(2,226)	(740)
Total deferred tax liabilities	(26,742)	(36,157)
Net deferred tax liabilities	(2,548)	$ (1,788)
Reclassification of unremitted foreign earnings	500
Reclassification of charitable contribution carryovers	$ 500