INCOME TAXES (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income Before Income Taxes [Abstract]
Domestic									$ 7,130	$ 15,305	$ 14,358
Foreign									63,308	55,892	54,236
Income before income taxes	$ 24,803	$ 20,692	$ 11,565	$ 13,378	$ 16,472	$ 13,927	$ 18,081	$ 22,717	70,438	71,197	68,594
U.S. federal and state [Abstract]
Current									609	6,496	8,978
Deferred									(1,465)	1,791	488
Total									(856)	8,287	9,466
Foreign [Abstract]
Current									11,737	7,686	9,565
Deferred									(292)	(922)	(1,188)
Total									11,445	6,764	8,377
Total U.S. and foreign	4,096	$ 1,990	$ 2,434	2,069	3,939	$ 4,041	$ 4,270	2,801	$ 10,589	$ 15,051	$ 17,843
Effective income tax rate reconciliation [Abstract]
Federal statutory rate									35.00%	35.00%	35.00%
U.S. benefits from research and experimentation activities									(3.50%)	(2.20%)	(0.60%)
State taxes, net of federal effect									(0.10%)	0.60%	0.80%
Foreign income at other than U.S. rates									(16.90%)	(21.40%)	(9.40%)
Executive compensation									0.00%	0.60%	0.40%
Share-based compensation									0.70%	0.10%	0.10%
Adjustment of prior amounts									0.00%	1.40%	0.10%
Taiwan Restructuring									0.00%	7.20%	0.00%
Domestic production deduction									(1.30%)	(1.30%)	(0.30%)
Other, net									1.10%	1.10%	(0.10%)
Provision for income taxes									15.00%	21.10%	26.00%
Undistributed earnings of foreign subsidiaries	188,899								$ 188,899
Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability, Undistributed Earnings of Foreign Subsidiaries	37,000								37,000
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Amount									928
Reconciliation of gross unrecognized tax benefits [Roll Forward]
Beginning balance				$ 1,773				$ 701	1,773	$ 701	$ 758
Additions for tax positions relating to the current fiscal year									364	194	59
Additions for tax positions relating to prior fiscal years									200	1,400	125
Settlements with taxing authorities									(248)	(522)	(207)
Lapse of statute of limitations									0	0	(34)
Ending balance	2,089				1,773				2,089	1,773	$ 701
Accrued interest and penalties on uncertain tax positions	65				47				65	47
Deferred tax assets [Abstract]
Employee benefits	4,612				4,061				4,612	4,061
Inventory	3,117				3,271				3,117	3,271
Bad debt reserve	615				391				615	391
Deferred Tax share-based compensation expense	8,262				9,863				8,262	9,863
Credit and other carryforwards	25,596				556				25,596	556
Depreciation and amortization	0				1,263				0	1,263
Other	1,487				3,599				1,487	3,599
Valuation allowance	(3,022)				(3,079)				(3,022)	(3,079)
Total deferred tax assets	40,667				19,925				40,667	19,925
Deferred tax liabilities [Abstract]
Depreciation and amortization	17,374				0				17,374	0
Translation adjustment	2,079				55				2,079	55
Other	542				339				542	339
Total deferred tax liabilities	$ 19,995				$ 394				$ 19,995	394
Carryforwards [Line Items]
Operating loss carryforwards expiration dates									fiscal year 2017 and fiscal year 2036
Tax credit carryforward expiration dates									fiscal years 2027 through 2037
Foreign income tax adjustment										$ 868
Diluted earnings per share effect of foreign income tax adjustment (in dollars per share)										$ 0.04
Tax holiday rate percentage	0.00%				0.00%				0.00%	0.00%	0.00%
Percentage of local statutory rate in effect for 2016	50.00%								50.00%
Percentage of local statutory rate in effect for 2017	50.00%								50.00%
Approximate tax provision reduction as a result in the tax holiday									$ 3,771	$ 5,446	$ 3,770
Tax Holiday approximate diluted earning per share benefit (in dollars per share)									$ 0.15	$ 0.22	$ 0.15
Capital Loss Carryforward [Member]
Carryforwards [Line Items]
Tax credit carryforward, amount	$ 2,795								$ 2,795
Tax credit carryforward, valuation allowance	2,795								$ 2,795
Internal Revenue Service (IRS) [Member]
Income Tax Examination [Line Items]
Tax periods open to examination by taxing authorities									fiscal years 2013 through 2016
Carryforwards [Line Items]
Net operating loss carryforwards	43,913								$ 43,913
Tax credit carryforward, amount	2,471								$ 2,471
State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Tax periods open to examination by taxing authorities									fiscal years 2012 through 2016
Carryforwards [Line Items]
Net operating loss carryforwards	35,910								$ 35,910
Tax credit carryforward, amount	2,151								2,151
Tax credit carryforward, valuation allowance	2,084								$ 2,084
Foreign Country [Member]
Income Tax Examination [Line Items]
Tax periods open to examination by taxing authorities									fiscal years 2012 through 2016
Carryforwards [Line Items]
Net operating loss carryforwards	4,736								$ 4,736
Operating loss carryforwards, valuation allowance	2,014								2,014
Tax credit carryforward, amount	$ 2,442								$ 2,442