CAPITAL STOCK, STOCK-BASED COMPENSATION AND BENEFIT PLAN - Equity Plans (Details)	Jun. 30, 2023 shares
Keryx Equity Plans(1)(2)*
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Awards outstanding (in shares)	287,100
Additional awards authorized for grant (in shares)	0
Akebia Therapeutics, Inc. Amended and Restated 2008 Equity Incentive Plan (the 2008 Plan)(2)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Awards outstanding (in shares)	419
Additional awards authorized for grant (in shares)	0
Akebia Therapeutics, Inc. 2014 Incentive Plan, as amended (2) (the 2014 Plan) (replaces 2008 Plan)
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Awards outstanding (in shares)	17,513,530
Additional awards authorized for grant (in shares)	0
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)	549,000
Additional awards authorized for grant (in shares)	16,256,679