Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2022	May 04, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q1
Trading Symbol	EPZM
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common stock, $0.0001 par value
Entity Registrant Name	EPIZYME, INC.
Entity Central Index Key	0001571498
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Entity Common Stock Shares Outstanding		164,874,549
Entity Shell Company	false
Entity File Number	001-35945
Entity Tax Identification Number	26-1349956
Entity Address, Address Line One	400 Technology Square, 4th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Incorporation, State or Country Code	DE
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	229-5872