Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 03, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $.01 Par Value
Trading Symbol	FORR
Security Exchange Name	NASDAQ
Entity Registrant Name	FORRESTER RESEARCH, INC.
Entity Central Index Key	0001023313
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		19,129,000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Incorporation, State or Country Code	DE
Entity File Number	000-21433
Entity Tax Identification Number	04-2797789
Entity Address, Address Line One	60 Acorn Park Drive
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02140
City Area Code	617
Local Phone Number	613-6000