STOCK-BASED COMPENSATION AND BENEFIT PLAN - Narrative (Details)		3 Months Ended
	Jun. 06, 2019 USD ($) shares	Mar. 31, 2024 USD ($) installment shares	Mar. 31, 2023 USD ($)	Dec. 31, 2023 shares
Class of Stock [Line Items]
Stock-based compensation expense | $		$ 2,360,000	$ 2,489,000
Granted (in shares)		4,088,450
Number of options outstanding (in shares)		16,877,776		13,312,835
Unrecognized compensation costs, options | $		$ 10,000,000
Unrecognized compensation costs, options, period for recognition		3 years 18 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)		4,545,480		4,637,801
Number of shares issued (in shares)		92,321
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)		970,950
Number of options outstanding (in shares)		970,950
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)		1,764,950		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 5 months 4 days
Unrecognized compensation costs, stock | $		$ 7,700,000
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)		3,117,500