Stockholders' Equity - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ 607,644	$ 553,690	$ 632,045
Ending Balance	717,832	607,644	553,690
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	15,213	15,166	5,898
Other comprehensive (loss) income before reclassifications	(1,637)	283	8,291
Amounts reclassified from accumulated other comprehensive income	11	(236)	977
Ending Balance	13,587	15,213	15,166
Currency Translation Adjustments
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	15,168	15,389	6,545
Other comprehensive (loss) income before reclassifications	(1,651)	(221)	8,844
Ending Balance	13,517	15,168	15,389
Unrealized Gains (Losses) on Available-for-Sale Securities
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(1)	(3)	103
Other comprehensive (loss) income before reclassifications	(110)	(10)	(231)
Amounts reclassified from accumulated other comprehensive income	(1)	12	125
Ending Balance	(112)	(1)	(3)
Pension Liability Adjustments
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	46	(220)	(750)
Other comprehensive (loss) income before reclassifications	124	514	(322)
Amounts reclassified from accumulated other comprehensive income	12	(248)	852
Ending Balance	$ 182	$ 46	$ (220)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount after tax, before reclassification adjustments of other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=84158357&loc=d3e1436-108581

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- Definition

Amount after tax of reclassification adjustments of other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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- Definition

Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4590271-111686

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