Debt instrument exchange amount.

No definition available.

Name:	kpti_DebtInstrumentExchangeAmount
Namespace Prefix:	kpti_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Remaining payments payable.

+ References

No definition available.

+ Details

Name:	kpti_RemainingPaymentsPayable
Namespace Prefix:	kpti_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Temporary reduction in minimum liquidity covenant.

+ References

No definition available.

+ Details

Name:	kpti_TemporaryReductionInMinimumLiquidityCovenant
Namespace Prefix:	kpti_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 55
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482925/835-30-45-2

+ Details

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in YYYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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+ Details

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

- Definition

Cash received on stock transaction after deduction of issuance costs.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockConsiderationReceivedOnTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Section 50
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-URI https://asc.fasb.org/1943274/2147483399/855-10-50-2

+ Details

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

- Definition

Date the event occurred after the balance sheet date but before financial statements are issues or available to be issued, in YYYY-MM-DD format.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Subparagraph (a)
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
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Period Type:	duration

Subsequent Event - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended		9 Months Ended
	Oct. 07, 2025	Oct. 31, 2025	May 31, 2024	Sep. 30, 2025	Dec. 31, 2024	May 13, 2024	Oct. 31, 2018
Subsequent Event [Line Items]
Debt instrument exchange amount			$ 148,000
Amended Revenue Interest Agreement [Member]
Subsequent Event [Line Items]
Aggregate principal amount			135,000
2029 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount				$ 116,000	$ 116,000	$ 5,000
2025 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount			$ 24,500	$ 24,500	$ 24,500		$ 172,500
Maturity date				Oct. 15, 2025
Subsequent Event [Member] \| 2029 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount	$ 101,000
Subsequent Event [Member] \| 2025 Notes [Member]
Subsequent Event [Line Items]
Debt instrument exchange amount		$ 24,300
Maturity date		Oct. 15, 2025
Subsequent Event [Member] \| 2028 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount	$ 15,000
Maturity date	Oct. 15, 2028
Subsequent Event [Member] \| New 2029 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount	$ 103,500
Subsequent Event [Member] \| Financing Transactions [Member]
Subsequent Event [Line Items]
Subsequent event date	Oct. 07, 2025
Temporary reduction in minimum liquidity covenant	$ 15,000
Maturity date	May 31, 2028
Subsequent Event [Member] \| Financing Transactions [Member] \| Maximum [Member] \| Amended Revenue Interest Agreement [Member]
Subsequent Event [Line Items]
Remaining payments payable	$ 116,200
Subsequent Event [Member] \| Financing Transactions [Member] \| Amended Term Loan [Member]
Subsequent Event [Line Items]
Aggregate principal amount	112,500
Subsequent Event [Member] \| Financing Transactions [Member] \| 2028 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount	15,000
Subsequent Event [Member] \| Financing Transactions [Member] \| New 2029 Notes [Member]
Subsequent Event [Line Items]
Aggregate principal amount	103,500
Subsequent Event [Member] \| Financing Transactions [Member] \| Common Stock [Member] \| 2029 Notes [Member]
Subsequent Event [Line Items]
Debt instrument exchange amount	15,000
Subsequent Event [Member] \| Financing Transactions [Member] \| Common Stock and Warrants [Member] \| Private Placement [Member]
Subsequent Event [Line Items]
Gross proceeds	8,800
Subsequent Event [Member] \| Financing Transactions [Member] \| Common Stock and Warrants [Member] \| 2025 Notes [Member]
Subsequent Event [Line Items]
Debt instrument exchange amount	24,300
Subsequent Event [Member] \| Financing Transactions [Member] \| Term Loan Borrowings [Member] \| Convertible Debt [Member]
Subsequent Event [Line Items]
Aggregate principal amount	27,500
Subsequent Event [Member] \| Financing Transactions [Member] \| Near Term Deferrals of Interest [Member] \| Royalty Payment [Member]
Subsequent Event [Line Items]
Aggregate principal amount	$ 25,400