STOCK-BASED COMPENSATION AND BENEFIT PLAN - Narrative (Details)		3 Months Ended		9 Months Ended
	Jun. 06, 2019 USD ($) shares	Sep. 30, 2024 USD ($) shares	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($) installment shares	Sep. 30, 2023 USD ($)	Dec. 31, 2023 shares
Class of Stock [Line Items]
Stock-based compensation expense | $		$ 1,646,000	$ 1,824,000	$ 6,078,000	$ 7,803,000
Granted (in shares)				5,200,050
Number of options outstanding (in shares)		16,755,825		16,755,825		13,312,835
Unrecognized compensation costs, options | $		$ 8,500,000		$ 8,500,000
Unrecognized compensation costs, options, period for recognition				2 years 9 months 14 days
2014 Employee Stock Purchase Plan
Class of Stock [Line Items]
Purchase price at the end of offering period	85.00%
Offering period	6 months
Maximum employee subscription rate	15.00%
Maximum employee subscription amount | $	$ 25,000
Maximum number of shares per employee in any offering period	1,500
Common stock, reserved for future issuance (in shares)		4,448,069		4,448,069		4,637,801
Number of shares issued (in shares)				189,732
Share-based Payment Arrangement, Option
Class of Stock [Line Items]
Expiration period				10 years
Share-based Payment Arrangement, Option | Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Class of Stock [Line Items]
Vesting percentage				100.00%
Share-based Payment Arrangement, Option | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting period				1 year
Vesting percentage				25.00%
Share-based Payment Arrangement, Option | Share Based Compensation Award Tranche Two
Class of Stock [Line Items]
Vesting period				1 year
Number of equal quarterly installments | installment				12
Share-based Payment Arrangement, Option | Minimum
Class of Stock [Line Items]
Vesting period				12 months
Share-based Payment Arrangement, Option | Maximum
Class of Stock [Line Items]
Vesting period				48 months
Stock appreciation rights
Class of Stock [Line Items]
Expiration period				10 years
Stock appreciation rights | Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Class of Stock [Line Items]
Vesting percentage				100.00%
Stock appreciation rights | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting period				1 year
Vesting percentage				25.00%
Stock appreciation rights | Share Based Compensation Award Tranche Two
Class of Stock [Line Items]
Vesting period				1 year
Number of equal quarterly installments | installment				12
Stock appreciation rights | Minimum
Class of Stock [Line Items]
Vesting period				12 months
Stock appreciation rights | Maximum
Class of Stock [Line Items]
Vesting period				48 months
Inducement Award Program
Class of Stock [Line Items]
Granted (in shares)				1,767,550
Number of options outstanding (in shares)		1,763,550		1,763,550
Inducement Award Program | Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Class of Stock [Line Items]
Number of options outstanding (in shares)		2,528,550		2,528,550		794,000
Unvested RSUs | Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Class of Stock [Line Items]
Vesting percentage				100.00%
Unvested RSUs | Share-Based Payment Arrangement, Tranche Two, Following First Anniversary After Grant Date
Class of Stock [Line Items]
Vesting period				2 years
Vesting percentage				66.67%
Number of equal quarterly installments | installment				8
Award vesting grace period				1 year
Unvested RSUs | Share-Based Payment Arrangement, Tranche One, First Anniversary After Grant Date, Subjected To Individual Continued Service
Class of Stock [Line Items]
Vesting percentage				33.33%
Unvested RSUs | Share-Based Payment Arrangement, Tranche Two, Second Anniversary After Grant Date, Subjected To Individual Continued Service
Class of Stock [Line Items]
Vesting percentage				33.33%
Unvested RSUs | Share-Based Payment Arrangement, Tranche Three, Third Anniversary After Grant Date, Subjected To Individual Continued Service
Class of Stock [Line Items]
Vesting percentage				33.33%
Unvested RSUs | Share-Based Payment Arrangement, Tranche One, First Anniversary After Grant Date
Class of Stock [Line Items]
Vesting percentage				33.33%
Restricted Stock Units (RSUs) And Performance Based Restricted Stock Units (PSUs)
Class of Stock [Line Items]
Unrecognized compensation costs, options, period for recognition				2 years 25 days
Unrecognized compensation costs, stock | $		$ 6,200,000		$ 6,200,000
Director | Share-based Payment Arrangement, Option | Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Class of Stock [Line Items]
Granted (in shares)				3,432,500