Document and Entity Information
Jul. 05, 2022
Document and Entity Information [Abstract]  
Document Type 8-K
Document Period End Date Jul. 05, 2022
Entity Registrant Name Amphastar Pharmaceuticals, Inc.
Entity Incorporation, State or Country Code DE
Entity File Number 001-36509
Entity Tax Identification Number 33-0702205
Entity Address, Address Line One 11570 6th Street
Entity Address, City or Town Rancho Cucamonga
Entity Address, State or Province CA
Entity Address, Postal Zip Code 91730
City Area Code 909
Local Phone Number 980-9484
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Title of 12(b) Security Common Stock, par value $0.0001 per share
Trading Symbol AMPH
Security Exchange Name NASDAQ
Entity Emerging Growth Company false
Entity Central Index Key 0001297184
Amendment Flag false