Percentage of eligible earnings withheld to participate in an offering under the ESPP.

No definition available.

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Namespace Prefix:	olma_
Data Type:	dtr-types:percentItemType
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Period Type:	duration

- Definition

Duration of offering period.

+ References

No definition available.

+ Details

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Namespace Prefix:	olma_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The period of time in which a "Purchase Period" lasts.

+ References

No definition available.

+ Details

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Namespace Prefix:	olma_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of purchase period of awards.

+ References

No definition available.

+ Details

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Namespace Prefix:	olma_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

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

- Definition

Purchase price of common stock expressed as a percentage of its fair value.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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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

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Namespace Prefix:
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Balance Type:
Period Type:

Stock-Based Compensation - 2020 Employee Stock Purchase Plan (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2022 USD ($) shares	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) shares	Sep. 30, 2021 USD ($)	Dec. 31, 2020 item
Stock-Based Compensation
Percent of common stock at fair market value to be exercised			100.00%
Stock-based compensation expense \| $	$ 4,275	$ 4,157	$ 13,968	$ 11,286
Employee stock purchase plan contingently issuable
Stock-Based Compensation
Percentage of eligible earnings withheld					15.00%
Percent of common stock at fair market value to be exercised					85.00%
Number of months for each purchase period					6 months
Number of purchase periods \| item					2
Common stock reserved for issuance \| shares	430,416		430,416
Stock-based compensation expense \| $	$ 100		$ 300
Employee stock purchase plan contingently issuable \| Maximum
Stock-Based Compensation
Offering period					27 months
2022 Inducement Plan
Stock-Based Compensation
Common stock reserved for issuance \| shares	2,000,000		2,000,000