Description of Business, Basis of Presentation and Significant Accounting Policies and Recently Issued Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business The 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 September 30, 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. The Company consolidated four branches during October 2021 to create a more efficient branch footprint. This consolidation reduced the number of branches from 53 to 49. The Company integrated these locations into other branches within its network.
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 nine months ended September 30, 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 management's estimate of the fair value of financial instruments. 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 year's net income or stockholders’ equity.
Investment Securities	Investment Securities Investment securities for which the Bank has the positive intent and ability to hold to maturity are classified as held to maturity and are carried at amortized cost. Investment securities held primarily for the purpose of selling in the near term are classified as trading securities and are reported at fair value, with unrealized gains and losses included in income. Investment securities not classified as held to maturity or trading are classified as available for sale and are reported at fair value with unrealized gains and losses, net of income taxes, as a separate component of other comprehensive income. The Bank determines the appropriate classification of investment securities at the time of purchase and reassesses the classification at each reporting date. When the Company acquires another entity, all investment securities are recorded at fair value and classified as available for sale at the acquisition date. Realized gains and losses on sales of investment securities are recorded on the trade date in gain on sale of investment securities, net on the Consolidated Statements of Income and determined using the specific identification method. Premiums and discounts on investment securities available for sale and held to maturity are amortized or accreted into income using the interest method. The objective of the interest method is to calculate periodic interest income at a constant effective yield. An investment security available for sale or held to maturity is placed on nonaccrual status at the time any principal or payments become more than 90 days delinquent and classified as past due after 30 days of nonpayment. Interest accrued, but not received for an investment security classified as nonaccrual is reversed against interest income during the period that the investment security is placed on nonaccrual status. ACL on Investment Securities Held to Maturity The Company measures expected credit losses on investment securities held to maturity on a pooled, collective basis by major investment security type with similar risk characteristics. A historical lifetime probability of default and severity of loss in the event of default is derived or obtained from external sources and adjusted for the expected effects of reasonable and supportable forecasts over the expected lives of the investment securities on those historical credit losses. Expected credit losses on investment securities in the held to maturity portfolio that do not share similar risk characteristics with any of the pools are individually measured based on net realizable value, or the difference between the discounted value of the expected future cash flows, based on the original effective interest rate, and the recorded amortized cost basis of the investment securities. Accrued interest receivable on investment securities held to maturity is excluded from the estimate of expected credit losses. Changes in the ACL on investment securities held to maturity are recorded as provision for credit losses expense. Losses are charged against the ACL when management believes the uncollectability of an investment security held to maturity is confirmed.
Recently Issued or Adopted Accounting Pronouncements	Recently Issued or Adopted Accounting Pronouncements FASB 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 on January 1, 2020 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 guidance for a limited period of time to ease the potential burden in accounting for (or recognizing the effects of) reference rate reform on financial reporting. The amendments in this ASU are effective for all entities as of March 12, 2020 through December 31, 2022. The amendments are elective, apply to all entities, and provide optional expedients and exceptions for applying GAAP to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. The Bank’s interest rate swap-related transactions are the majority of the Company's LIBOR exposure. Effective January 25, 2021, the Company adhered 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 does not expect this ASU to have a material impact on its business operations and the Condensed Consolidated Financial Statements.
ACL on Investment Securities	ACL on Investment Securities The Company evaluated investment securities available for sale as of September 30, 2021 and December 31, 2020 and determined that any declines in fair value were attributable to changes in interest rates relative to where these investments fall within the yield curve and individual characteristics. Management monitors published credit ratings for adverse changes for all rated investment securities and none of these securities had a below investment grade credit rating as of both September 30, 2021 and December 31, 2020. In addition, the Company does not intend to sell these securities nor does the Company consider it more likely than not that it will be required to sell these securities before the recovery of the amortized cost basis, which may be upon maturity. Therefore, no ACL on investment securities available for sale was recorded as of September 30, 2021 and December 31, 2020. The Company also evaluated investment securities held to maturity for current expected credit losses. There were no investment securities held to maturity classified as nonaccrual or past due as of September 30, 2021 and all were issued by the U.S. government and its agencies and either explicitly or implicitly guaranteed by the U.S. government, highly rated by major credit rating agencies and have a long history of no credit losses. Accordingly, the Company did not measure expected credit losses on investment securities held to maturity since the historical credit loss information adjusted for current conditions and reasonable and supportable forecasts results in an expectation that nonpayment of the amortized cost basis is zero. Therefore, no ACL on investment securities held to maturity was recorded as of September 30, 2021.