Marketable Securities (Amortized Cost and Fair Value of Marketable Securities) (Details) - USD ($) $ in Thousands	Mar. 30, 2019	Sep. 30, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 56,524	$ 56,364
Gross unrealized gains	52	0
Gross unrealized losses	(161)	(413)
Fair value	56,415	55,951
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		220
Gross unrealized gains		0
Gross unrealized losses		(1)
Fair value		219
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,975
Gross unrealized gains	0
Gross unrealized losses	0
Fair value	1,975
Corporate notes/bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	53,546	55,140
Gross unrealized gains	52	0
Gross unrealized losses	(159)	(403)
Fair value	53,439	54,737
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,003	1,004
Gross unrealized gains	0	0
Gross unrealized losses	(2)	(9)
Fair value	$ 1,001	$ 995

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
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-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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