Debt conversion, converted instrument, of pre funded warrants.

No definition available.

Name:	kpti_DebtConversionConvertedInstrumentOfPreFundedWarrants
Namespace Prefix:	kpti_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility, date of last required payment.

+ References

No definition available.

+ Details

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Namespace Prefix:	kpti_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-Publisher FASB
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The number of shares issued in exchange for the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or payments in the period.

+ References

+ Details

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

- Definition

The price per share of the conversion feature embedded in the debt instrument.

+ References

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-SubTopic 20
-Name Accounting Standards Codification
-Section 50
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

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

- Definition

The average effective interest rate during the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
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+ Details

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

- Definition

Description of the frequency of the required periodic payments of interest, principal, or both, and the amount, if set, or a description of a formula upon which payment is based.

+ References

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+ Details

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

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kpti_NewTwoThousandTwentyNineNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kpti_TwoThousandTwentyNineAndNewTwoThousandTwentyNineNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Event - 2029 Notes - Additional Information (Detail) - USD ($)		1 Months Ended	9 Months Ended
	Oct. 07, 2025	Oct. 31, 2025	Sep. 30, 2025	Dec. 31, 2024	May 13, 2024
Convertible Note Offering [Member]
Subsequent Event [Line Items]
Notes converted in to common stock, amount			4.2049
Notes, conversion price per share			$ 237.82
Notes converted in to common stock, shares			$ 1,000
2029 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount			$ 116,000,000	$ 116,000,000	$ 5,000,000
Notes, interest rate			6.00%
2029 Notes [Member] \| Convertible Note Offering [Member]
Subsequent Event [Line Items]
Notes converted in to common stock, amount			29.6296
Notes, conversion price per share			$ 33.75
Notes converted in to common stock, shares			$ 1,000
Subsequent Event [Member] \| 2029 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount	$ 101,000,000
Subsequent Event [Member] \| 2029 Notes [Member] \| Convertible Note Offering [Member]
Subsequent Event [Line Items]
Notes converted in to common stock, shares		$ 15,000,000
Subsequent Event [Member] \| 2029 Notes [Member] \| Convertible Note Offering [Member] \| Common Stock [Member]
Subsequent Event [Line Items]
Notes converted in to common stock, amount		2,024,344
Pre-funded warrants to common stock		552,164
Subsequent Event [Member] \| New 2029 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount	$ 103,500,000
Notes, interest rate	9.00%
Subsequent Event [Member] \| New 2029 Notes [Member] \| Convertible Note Offering [Member]
Subsequent Event [Line Items]
Notes converted in to common stock, amount	44.444
Notes, conversion price per share	$ 22.5
Notes converted in to common stock, shares	$ 1,000
Subsequent Event [Member] \| 2029 Notes and New 2029 Notes [Member]
Subsequent Event [Line Items]
Interest, payment terms	Interest on the New 2029 Notes incurred through March 31, 2026 will be payable in-kind. Interest incurred after March 31, 2026 will be payable in cash on the applicable payment date.
Date of last required payment	Mar. 31, 2026