STOCK-BASED COMPENSATION AND BENEFIT PLAN - Equity Plans (Details) - shares	Jun. 30, 2024	Dec. 31, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of options outstanding (in shares)	17,278,820	13,312,835
Inducement Award Program
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of options outstanding (in shares)	1,604,950
Keryx Equity Plans
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Awards outstanding (in shares)	208,986	232,203
Additional awards authorized for grant (in shares)	0	0
Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (the 2014 Plan) (replaces 2008 Plan)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Awards outstanding (in shares)	12,597,753	15,311,501
Additional awards authorized for grant (in shares)	0	0
Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (the 2014 Plan) (replaces 2008 Plan) | Inducement Award Program
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of options outstanding (in shares)	1,496,428	1,616,019
Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Awards outstanding (in shares)	10,435,850	1,712,400
Additional awards authorized for grant (in shares)	0	17,382,722
Akebia Therapeutics, Inc. 2023 Stock Incentive Plan (the 2023 Plan) (replaces 2014 Plan) | Inducement Award Program
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of options outstanding (in shares)	2,374,950	794,000