Lessor Leases - Sale-Type Lease Receivable Components (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Dec. 31, 2018
Capital Leased Assets [Line Items]
Total future minimum sales-type lease payments	$ 33,279	$ 28,295
Present value adjustment	(3,047)	(2,477)
Net investment in sales-type leases	30,232	25,818
Less: Current portion	(9,191)	(8,736)
Long-term net investment in sales-type leases	$ 21,041	17,082
Minimum
Capital Leased Assets [Line Items]
Terms of sales-type leases (in years)	1 year
Maximum
Capital Leased Assets [Line Items]
Terms of sales-type leases (in years)	5 years
Allowance For Credit Losses
Capital Leased Assets [Line Items]
Sales-type Lease, Lease Receivable	$ 200	$ 200

Lessor Leasing Arrangements, Sales-Type Leases, Term of Contract

No definition available.

Name:	omcl_LessorLeasingArrangementsSalesTypeLeasesTermofContract
Namespace Prefix:	omcl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Amount of net investment in sales-type and direct financing lease, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77888421&loc=SL77919306-209978

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=77888421&loc=SL77919308-209978

+ Details

Name:	us-gaap_NetInvestmentInLeaseCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of net investment in sales-type and direct financing lease, classified as noncurrent.

+ References

+ Details

Name:	us-gaap_NetInvestmentInLeaseNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Present value of lease payments not yet received by lessor and amount expected to be derived from underlying asset, following end of lease term guaranteed by lessee or other third party unrelated to lessor, from sales-type and direct financing leases.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=119202524&loc=SL77919391-209981

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=119202524&loc=SL77919379-209981

+ Details

Name:	us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of undiscounted cash flows to be received by lessor for sales-type and direct financing leases.

+ References

+ Details

Name:	us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivablePaymentsToBeReceived
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of undiscounted lease receivable in excess of discounted receivable for sales-type and direct financing leases.

+ References

+ Details

Name:	us-gaap_SalesTypeAndDirectFinancingLeasesLeaseReceivableUndiscountedExcessAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=119202524&loc=SL77919379-209981

+ Details

Name:	us-gaap_SalesTypeLeaseLeaseReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=omcl_AllowanceForCreditLossesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: