Restructuring charges (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2018	Dec. 30, 2017	Apr. 01, 2017	Dec. 31, 2016	Mar. 31, 2018	Apr. 01, 2017
Restructuring Reserve [Roll Forward]
Starting balance	$ 1,175	$ 1,301	$ 2,359	$ 0	$ 1,301	$ 0
Provision	726	1,164	557	7,062
Payments and other	(968)	(1,290)	(951)	(4,703)
Ending balance	933	1,175	1,965	2,359	933	1,965
Severance Related
Restructuring Reserve [Roll Forward]
Starting balance	1,175	1,301	2,359	0	1,301	0
Provision	599	629	319	2,703
Payments and other	(841)	(755)	(892)	(344)
Ending balance	933	1,175	1,786	2,359	933	1,786
Severance Related \| Industrial Lasers & Systems
Restructuring Reserve [Roll Forward]
Restructuring cost incurred	600		300		1,000	7,100
Severance Related \| OEM Laser Sources
Restructuring Reserve [Roll Forward]
Restructuring cost incurred	100		300		900	500
Severance Related \| Other current liabilities:
Restructuring Reserve [Roll Forward]
Ending balance	900				900
Asset Write-Offs
Restructuring Reserve [Roll Forward]
Starting balance	0	0	0	0	0	0
Provision	9	430	(45)	4,359
Payments and other	(9)	(430)	45	(4,359)
Ending balance	0	0	0	0	0	0
Other
Restructuring Reserve [Roll Forward]
Starting balance	0	0	0	0	0	0
Provision	118	105	283	0
Payments and other	(118)	(105)	(104)	0
Ending balance	$ 0	$ 0	$ 179	$ 0	$ 0	$ 179

Restructuring related payment and other during the period

No definition available.

Name:	cohr_Restructuringrelatedpaymentandotherduringtheperiod
Namespace Prefix:	cohr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Discloses the amount charged against the accrued restructuring reserves, or earnings if not previously accrued, during the period for the specified type of restructuring cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.P.4(b))
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

+ Details

Name:	us-gaap_RestructuringAndRelatedCostIncurredCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of known and estimated obligations associated with exit from or disposal of business activities or restructurings pursuant to a duly authorized plan, which are expected to be paid in the next twelve months or in the normal operating cycle if longer. Costs of such activities include those for one-time termination benefits, termination of an operating lease or other contract, consolidating or closing facilities, relocating employees, and costs associated with an ongoing benefit arrangement, but excludes costs associated with the retirement of a long-lived asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 5.P.4(b)(2))
-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 420
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

+ Details

Name:	us-gaap_RestructuringReserveCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of increase (decrease) in the accrual for restructuring costs.

+ References

+ Details

Name:	us-gaap_RestructuringReservePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_RestructuringReserveRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RestructuringCostAndReserveAxis=us-gaap_EmployeeSeveranceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=cohr_IndustrialLasersSystemsMemberDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=cohr_OEMLaserSourceMemberDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherCurrentLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RestructuringCostAndReserveAxis=cohr_AssetwriteoffsDomain
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RestructuringCostAndReserveAxis=us-gaap_OtherRestructuringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: