Segment Information - Sales and Income (Loss) from Operations (Details) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2018 USD ($)	Apr. 01, 2017 USD ($)	Mar. 31, 2018 USD ($) segments	Apr. 01, 2017 USD ($)
Segment Reporting [Abstract]
Number of reporting segments \| segments			2
Segment Reporting Information [Line Items]
Net sales:	$ 481,118	$ 422,833	$ 958,683	$ 768,906
Income from operations before other income, income taxes and loss from discontinued operations	100,661	71,089	209,984	113,289
Total other income (expense), net	(9,510)	(10,255)	(18,010)	(5,083)
Income from continuing operations before income taxes	91,151	60,834	191,974	108,206
OEM Laser Sources
Segment Reporting Information [Line Items]
Net sales:	317,138	277,144	642,795	515,880
Income (loss) from continuing operations:	117,120	102,870	244,837	186,460
Industrial Lasers & Systems
Segment Reporting Information [Line Items]
Net sales:	163,980	145,689	315,888	253,026
Income (loss) from continuing operations:	1,173	(11,571)	2,385	(28,079)
Corporate and other
Segment Reporting Information [Line Items]
Income (loss) from continuing operations:	$ (17,632)	$ (20,210)	$ (37,238)	$ (45,092)

Income from operations before other income, income taxes and loss from discontinued operations

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Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68072869&loc=d3e41242-110953

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(15))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(8))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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The net result for the period of deducting operating expenses from operating revenues.

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The net amount of other operating income and expenses, the components of which are not separately disclosed on the income statement, from items that are associated with the entity's normal revenue producing operations.

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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