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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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The highest quantity of shares an employee can purchase under the plan per period.

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Balance Type:
Period Type:

STOCK-BASED COMPENSATION AND EMPLOYEE RETIREMENT PLANS - Narrative (Details) $ in Thousands		12 Months Ended
	Jun. 06, 2019 USD ($) shares	Dec. 31, 2025 USD ($) installment age shares	Dec. 31, 2024 USD ($) shares	Dec. 31, 2023 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 11,283	$ 7,775	$ 9,317
Granted (in shares) \| shares		5,464,077
Number of options outstanding (in shares) \| shares		18,152,258	16,684,325
Options exercised, aggregate intrinsic value		$ 1,800	$ 400	0
Fair value of options vested		4,300	3,700	6,400
Unrecognized compensation costs, options		$ 11,200
Unrecognized compensation costs, options, period for recognition (in years)		2 years 7 months 20 days
Employees eligibility age to participate in retirement plan \| age		21
Employers contributions to defined contribution plan		$ 1,900	1,700	1,700
2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 168	$ 84	73
Purchase price at the end of offering period	85.00%
Offering period (in months)	6 months
Maximum employee subscription rate (as percent)	15.00%
Maximum employee subscription amount	$ 25
Maximum number of shares per employee in offering period \| shares	1,500
Common stock, shares reserved for future issuance (in shares) \| shares		4,260,647	4,448,069
Number of shares issued (in shares) \| shares		187,422
Share-based Payment Arrangement, Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 5,356	$ 4,036	5,310
Expiration period (in years)		10 years
Share-based Payment Arrangement, Option \| Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		100.00%
Share-based Payment Arrangement, Option \| Share Based Compensation Award Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Vesting percentage		25.00%
Share-based Payment Arrangement, Option \| Share Based Compensation Award Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Number of equal quarterly installments \| installment		12
Share-based Payment Arrangement, Option \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		12 months
Share-based Payment Arrangement, Option \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		48 months
Stock appreciation rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period (in years)		10 years
Stock appreciation rights \| Share Based Compensation Award Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Vesting percentage		25.00%
Stock appreciation rights \| Share Based Compensation Award Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
Number of equal quarterly installments \| installment		12
Stock appreciation rights \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		12 months
Stock appreciation rights \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		48 months
Inducement Award Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) \| shares		1,454,477
Number of options outstanding (in shares) \| shares		1,152,477
Inducement Award Program \| Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding (in shares) \| shares		3,034,085	2,534,775
Unvested restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 5,214	$ 3,655	3,637
Unvested restricted stock units \| Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		100.00%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche One, First Anniversary After Grant Date, Subjected To Individual Continued Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		33.33%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche Two, Second Anniversary After Grant Date, Subjected To Individual Continued Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		33.33%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche Three, Third Anniversary After Grant Date, Subjected To Individual Continued Service
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		33.33%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche One, First Anniversary After Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		33.33%
Unvested restricted stock units \| Share-Based Payment Arrangement, Tranche Two, Following First Anniversary After Grant Date
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		2 years
Vesting percentage		66.67%
Number of equal quarterly installments \| installment		8
Award vesting grace period (in years)		1 year
Unvested restricted stock units \| Share Based Compensation Award Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		50.00%
Unvested restricted stock units \| Share Based Compensation Award Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		6 months
Vesting percentage		25.00%
Award vesting grace period (in years)		1 year
Restricted Stock Units (RSUs) And Performance Based Restricted Stock Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs, options, period for recognition (in years)		1 year 8 months 23 days
Vested in period		$ 3,400	$ 3,200	$ 8,400
Unrecognized compensation costs, stock		$ 7,700
Employees \| Share-based Payment Arrangement, Option \| Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) \| shares		3,634,300
Director \| Share-based Payment Arrangement, Option \| Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) \| shares		375,200