Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 12, 2021	Jun. 30, 2020
Cover [Abstract]
Entity Registrant Name	FIRST BANCORP.
Entity Central Index Key	0001057706
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock Shares Outstanding		218,228,695
Entity Emerging Growth Company	false
Entity Small Business	false
Trading Symbol	FBP
Entity Current Reporting Status	Yes
Entity Shell Company	false
Document Transition Report	false
Entity File Number	001-14793
Entity Tax Identification Number	66-0561882
Entity Address Address Line 1	1519 Ponce de León Avenue, Stop 23
Entity Address City Or Town	Santurce
Entity Address Country	PR
Entity Address Postal Zip Code	00908
City Area Code	787
Local Phone Number	729-8200
Security 12b Title	Common Stock ($0.10 par value)
Security Exchange Name	NYSE
Entity Interactive Data Current	Yes
Entity Incorporation State Country Code	PR
Entity Well Known Seasoned Issuer	Yes
Entity Public Float			$ 1,173,527,344
Entity Voluntary Filers	No
Document Annual Report	true
Documents Incorporated By Reference TextBlock	Portions of the definitive proxy statement relating to the registrant’s annual meeting of stockholders scheduled to be held on May 21, 2021 are incorporated by reference in response to items 10, 11, 12, 13 and 14 of Part III of this Form 10-K.