INVENTORIES AND PREPAID MANUFACTURING - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Inventory [Line Items]
Write-down of inventory	$ 590	$ 335
Benefit in cost of goods sold related to previously written down as excess inventory	3,700
Auryxia Drug Substance
Inventory [Line Items]
Prepaid manufacturing costs	0		$ 500
Write-down of inventory	600	$ 300
Vadadustat Drug Substance
Inventory [Line Items]
Prepaid manufacturing costs	$ 14,000		$ 14,000