Aggregate offering price.

No definition available.

Name:	kpti_AggregateOfferingPrice
Namespace Prefix:	kpti_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Commission percentage on gross proceeds from sale of shares.

+ References

No definition available.

+ Details

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Equity offering.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of authorized capital units or capital shares. This element is relevant to issuers of face-amount certificates and registered investment companies.

+ References

No definition available.

+ Details

Name:	us-gaap_CapitalUnitsAuthorized
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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

+ References

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+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash inflow from the additional capital contribution to the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of new stock issued during the period.

+ References

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Balance Type:	na
Period Type:	duration

- Definition

Reduction in the number of shares during the period as a result of a reverse stock split.

+ References

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- Details

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- Details

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Stockholders' Equity - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Feb. 25, 2025	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Jan. 30, 2025	Dec. 31, 2024	Feb. 17, 2023
Equity Offering [Line Items]
Common stock, shares authorized		53,333,000		53,333,000			53,333,000
Common Stock [Member]
Equity Offering [Line Items]
Number of shares of common stock issued			458,000		458,000
Open Market Sale Agreement [Member] \| Common Stock [Member]
Equity Offering [Line Items]
Net proceeds from sale of common stock				$ 100.0
Jefferies LLC [Member] \| Open Market Sale Agreement [Member] \| Common Stock [Member]
Equity Offering [Line Items]
Number of shares of common stock issued		0	0	0	0
Maximum [Member]
Equity Offering [Line Items]
Capital stock, shares authorized						805,000,000
Common stock, shares authorized						800,000,000
Common stock, shares authorized , reverse stock splits	800,000,000
Maximum [Member] \| Jefferies LLC [Member] \| Open Market Sale Agreement [Member]
Equity Offering [Line Items]
Aggregate offering price								$ 100.0
Percentage of commission of gross proceeds from the sale of Shares				3.00%
Minimum [Member]
Equity Offering [Line Items]
Capital stock, shares authorized						405,000,000
Common stock, shares authorized						400,000,000
Common stock, shares authorized , reverse stock splits	53,333,333