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Income Taxes - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2015 | Mar. 31, 2015 | Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2014
Income Tax Contingency [Line Items] |  |  |  |  |  |
Effective tax rate |  |  | 44.00% | 13.00% | 59.00% |
Release of a FIN 48 reserve related to the federal research and development tax credit |  |  | $ 1,219 | $ 1,046 | $ 784 | $ 4,026
Undistributed earnings of foreign subsidiaries |  |  | 22,200 |  |  |
Operating loss carryforwards, valuation allowance |  |  |  |  | 9,300 |
Valuation allowance related to deferred tax assets |  |  | $ 8,767 | 8,439 |  |
Tax benefit |  | $ 4,100 |  |  |  |
Decrease in unrecognized tax benefits due to expiration of certain federal statutes of limitations |  |  | 11.00% |  |  |
R&D Tax Credit |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Retroactive tax benefit | $ 800 |  | $ 900 |  | $ 600 |
Release of a FIN 48 reserve related to the federal research and development tax credit |  |  |  | $ 4,100 |  |

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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32537-109319 + Details
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- Definition Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to domestic income tax settlement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32698-109319 + Details
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