COVER PAGE - shares	3 Months Ended
	Mar. 31, 2020	Apr. 13, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	1-11859
Entity Registrant Name	PEGASYSTEMS INC.
Entity Incorporation, State or Country Code	MA
Entity Tax Identification Number	04-2787865
Entity Address, Address Line One	One Rogers Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142-1209
City Area Code	617
Local Phone Number	374-9600
Title of 12(b) Security	Common Stock, $.01 par value per share
Trading Symbol	PEGA
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		80,089,203
Amendment Flag	false
Entity Central Index Key	0001013857
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31