Description of Business, Basis of Presentation and Significant Accounting Policies and Recently Issued Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of BusinessThe Company is primarily engaged in the business of planning, directing and coordinating the business activities of its wholly-owned subsidiary, Heritage Bank. The Bank is headquartered in Olympia, Washington and conducts business from its 53 branch offices as of March 31, 2021 located throughout Washington State and the greater Portland, Oregon area. The Bank’s business consists primarily of commercial lending and deposit relationships with small and medium-sized businesses and their owners in its market areas and attracting deposits from the general public. The Bank also makes real estate construction and land development loans, consumer loans and originates first mortgage loans on residential properties primarily located in its market areas. The Bank's deposits are insured by the FDIC.
Basis of Presentation	Basis of Presentation The accompanying unaudited Condensed Consolidated Financial Statements have been prepared in accordance with GAAP for interim financial information and pursuant to the rules and regulations of the SEC. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. It is recommended that these unaudited Condensed Consolidated Financial Statements and accompanying Notes be read with the audited Consolidated Financial Statements and the accompanying Notes included in the 2020 Annual Form 10-K. In management's opinion, all adjustments (consisting only of normal recurring adjustments) considered necessary for a fair presentation have been included. Operating results for the three months ended March 31, 2021 are not necessarily indicative of the results that may be expected for the year ending December 31, 2021. To prepare unaudited Condensed Consolidated Financial Statements in conformity with GAAP, management makes estimates and assumptions based on available information. These estimates and assumptions affect the amounts reported in the financial statements and the disclosures provided. Management believes that the judgments, estimates, and assumptions used in the preparation of the Condensed Consolidated Financial Statements are appropriate based on the facts and circumstances at the time. Actual results, however, could differ significantly from those estimates. Material estimates that are particularly susceptible to significant change relate to management's estimate of ACL on loans, management's estimate of ACL on unfunded commitments, management's evaluation of goodwill impairment and the fair value of financial instruments. It is reasonably possible that management's estimate of the ACL on loans of $64.2 million at March 31, 2021 as disclosed in Note (4) Allowance for Credit Losses on Loans, management's estimate of the ACL on unfunded commitments of $3.6 million as disclosed in Note (14) Commitments and Contingencies, management's conclusion that the fair value of the reporting unit more likely than not exceeds its carrying value at March 31, 2021 as disclosed in Note (6) Goodwill and Other Intangible Assets and the estimates of fair value of financial instruments as disclosed in Note (12) Fair Value Measurements could materially change. In particular, these estimates have been and will continue to be affected by the ongoing COVID-19 pandemic. The severity, magnitude and duration, as well as the economic consequences of the COVID-19 pandemic, are uncertain, rapidly changing and difficult to predict. As a result, our accounting estimates and assumptions may change over time in response to the COVID-19 pandemic. The accompanying Condensed Consolidated Financial Statements include the accounts of the Company and its wholly-owned subsidiary, the Bank. All significant intercompany balances and transactions among the Company and the Bank have been eliminated in consolidation. Certain prior year amounts in the Condensed Consolidated Statements of Income and the Condensed Consolidated Statements of Cash Flows have been reclassified to conform to the current year’s presentation. Reclassifications had no effect on the prior years' net income or stockholders’ equity.
Recently Issued Accounting Pronouncements	Recently Issued or Adopted Accounting PronouncementsFASB ASU 2016-13, Financial Instruments: Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, as amended by ASU 2018-19, ASU 2019-04, ASU 2019-05, ASU 2019-10, ASU 2019-11, and ASU 2020-02, was originally issued in June 2016. This ASU replaced the incurred loss methodology with an expected loss methodology, which is commonly referred to as the "CECL" methodology. The measurement of expected credit losses under the CECL methodology is applicable to financial assets measured at amortized cost, including loans receivable. It also applies to off-balance sheet credit exposures such as loan commitments, standby letters of credit, financial guarantees, and other similar instruments. In addition, CECL Adoption made changes to the accounting for credit losses on investment securities available for sale. This ASU requires financial assets measured at amortized cost basis to be presented at the net amount expected to be collected. For public business entities, this ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years with early adoption permitted for fiscal years after December 15, 2018 and can be delayed under a provision of the CARES Act until the end of the official health emergency declaration. The Bank adopted ASU 2016-13 using the modified retrospective method for all financial assets measured at amortized cost and unfunded commitments. At adoption, the Bank elected not to measure an ACL on accrued interest receivable on loans receivable or accrued interest receivable on investment securities available for sale as Bank policy is to reverse interest income for uncollectible accrued interest receivable balances in a timely manner. The adoption of ASU 2016-13 included an increase to the ACL on loans of $3.4 million and an increase to the ACL on unfunded commitments of $3.7 million, resulting in a pretax cumulative-effect adjustment of $7.1 million. The impact of this adjustment to beginning retained earnings on January 1, 2020 was $5.6 million, net of tax. FASB ASU 2020-04, Reference Rate Reform (Topic 848), as amended by ASU 2021-01, was issued in March 2020 and provides optional expedients and exceptions for applying GAAP to loan and lease agreements, derivative contracts, and other transactions affected by the anticipated transition away from LIBOR toward new interest rate benchmarks. For transactions that are modified because of reference rate reform and that meet certain scope guidance (i) modifications of loan agreements should be accounted for by prospectively adjusting the effective interest rate and the modification will be considered "minor" so that any existing unamortized origination fees/costs would carry forward and continue to be amortized and (ii) modifications of lease agreements should be accounted for as a continuation of the existing agreement with no reassessments of the lease classification and the discount rate or remeasurements of lease payments that otherwise would be required for modifications not accounted for as separate contracts. ASU 2020-04 also provides numerous optional expedients for derivative accounting and is effective March 12, 2020 through December 31, 2022. An entity may elect to apply the ASU for contract modifications as of January 1, 2020, or prospectively from a date within an interim period that includes or is subsequent to March 12, 2020, up to the date that the financial statements are available to be issued. Once elected for a Topic or an Industry Subtopic within the Codification, the amendments in this ASU must be applied prospectively for all eligible contract modifications for that Topic or Industry Subtopic. The Bank’s swap related transactions are the majority of the Company's LIBOR exposure. Effective January 25, 2021, the Company has agreed to adhere to the Interbank Offered Rate Fallbacks Protocol as published by the International Swaps and Derivatives Association, Inc. and recommended by the Alternative Reference Rates Committee. The Company further anticipates this ASU will simplify any modifications executed between the selected start date (yet to be determined) and December 31, 2022 that are directly related to LIBOR transition by allowing prospective recognition of the continuation of the contract, rather than extinguishment of the old contract resulting in writing off unamortized net deferred fees. The Company does not expect this ASU to have a material impact on its business operations and the Condensed Consolidated Financial Statements.