Cover Page	3 Months Ended
	Mar. 31, 2020 shares
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	000-29480
Entity Registrant Name	HERITAGE FINANCIAL CORP
Entity Central Index Key	0001046025
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Incorporation, State or Country Code	WA
Entity Tax Identification Number	91-1857900
Entity Address, Address Line One	201 Fifth Avenue SW,
Entity Address, City or Town	Olympia
Entity Address, State or Province	WA
Entity Address, Postal Zip Code	98501
City Area Code	360
Local Phone Number	943-1500
Title of 12(b) Security	Common stock, no par value
Trading Symbol	HFWA
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	35,888,494