Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 26, 2020
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-14585
Entity Registrant Name	FIRST HAWAIIAN, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	99-0156159
Entity Address, Address Line One	999 Bishop Street, 29th Floor
Entity Address, City or Town	Honolulu
Entity Address, Postal Zip Code	96813
Local Phone Number	525-7000
City Area Code	808
Title of 12(b) Security	Common Stock
Trading Symbol	FHB
Security Exchange Name	NASDAQ
Entity Address, State or Province	HI
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		130,787,765
Current Fiscal Year End Date	--12-31
Entity Central Index Key	0000036377
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false