Cover Page - shares	9 Months Ended
	Sep. 30, 2020	Nov. 05, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Registrant Name	CATALYST PHARMACEUTICALS, INC.
Entity Central Index Key	0001369568
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Filer Category	Accelerated Filer
Trading Symbol	CPRX
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Address, State or Province	FL
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		103,648,224
Entity Tax Identification Number	76-0837053
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	355 Alhambra Circle
Entity Address, Address Line Two	Suite 1250
Entity Address, City or Town	Coral Gables
Entity Address, Postal Zip Code	33134
City Area Code	305
Local Phone Number	420-3200
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	001-33057