Employee Benefit Plans	12 Months Ended
Dec. 31, 2018
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans (a) 401(k) Plan The Company provides its eligible employees with a 401(k) plan called "Heritage Financial Corporation 401(k) Profit Sharing Plan and Trust" (the “Plan”). The Company funds certain Plan costs as incurred. The Plan includes the Company’s salary savings 401(k) plan for its employees. All employees hired may participate in the Plan the first of the month following thirty days of service. Participants may contribute a portion of their salary, which is matched by the Company at 50%, not to be greater than 3% of eligible compensation, up to certain Internal Revenue Service limits. A Roth feature was added to the plan in 2016. All participants are 100% vested in all accounts at all times. Employer matching contributions for the years ended December 31, 2018, 2017 and 2016 were $1.4 million, $1.1 million and $1.0 million, respectively. The profit sharing portion of the Plan is a defined contribution retirement plan. All profit sharing and discretionary contributions are completely discretionary. Participants are eligible for profit sharing contributions upon credit of 1,000 hours of service during the plan year, the attainment of 18 years of age, and employment on the last day of the year. Employees are vested in profit sharing contributions in the same manner as employer matching contributions discussed above. For the years ended December 31, 2018, 2017 and 2016, the Company made no employer profit sharing contributions. (b) Employment Agreements The Company has entered into contracts with certain senior officers that provide benefits under certain conditions following termination without cause, and/or following a change in control of the Company. (c) Deferred Compensation Plan During 2012, the Company adopted a Deferred Compensation Plan, which provides its directors and select executive officers with the opportunity to defer current compensation. Under the Plan, participants are permitted to elect to defer compensation and the Company has the discretion to make additional contributions to the Plan on behalf of any participant based on a number of factors. Compensation expense under the Deferred Compensation Plan totaled $810,000, $652,000 and $540,000 for the years ended December 31, 2018, 2017 and 2016, respectively. The Company’s contributions totaled $583,000, $453,000 and $521,000 for the years ended December 31, 2018, 2017 and 2016, respectively. As of December 31, 2018 and 2017, the carrying value of the obligation related to the deferred compensation plans was $3.7 million and $2.8 million, respectively. (d) Split-Dollar Life Insurance Benefit Plan In conjunction with the Washington Banking Merger, the Company assumed the split-dollar life insurance benefit plan previously maintained by Washington Banking. Life insurance policies are maintained for current or former officers of the Bank or former Washington Banking officers that are subject to split-dollar life insurance agreements, which continue after the participant's employment and retirement. All participants are fully vested in their split-dollar life insurance benefits. The accrued benefit liability for the split-dollar life insurance agreements represents the present value of the future death benefits payable to the participants' beneficiaries. The split-dollar life insurance projected benefit obligation is included in accrued expenses and other liabilities on the Company's Consolidated Statements of Financial Condition. As of December 31, 2018 and 2017, the carrying value of the obligation was $268,000 and $250,000, respectively. (e) Salary Continuation Plan In conjunction with the Premier Merger, the Company assumed an unfunded deferred compensation plan for select former Premier Commercial executive officers, some of which are current Heritage officers. Under the Salary Continuation Plan, the Company will pay each participant, or their beneficiary, specified benefits over specified periods beginning with the individual's termination of service due to retirement subject to early termination provisions. A liability is accrued for the obligation under this plan. As of December 31, 2018, the carrying value of the obligation was $4.6 million. The expense incurred for the Salary Continuation Plan was $184,000 during the year ended December 31, 2018. There was no expense incurred for the Salary Continuation Plan during the years ended December 31, 2017 and 2016.

Employee Benefit Plans

(a) 401(k) Plan

The Company provides its eligible employees with a 401(k) plan called "Heritage Financial Corporation 401(k) Profit Sharing Plan and Trust" (the “Plan”). The Company funds certain Plan costs as incurred.

The Plan includes the Company’s salary savings 401(k) plan for its employees. All employees hired may participate in the Plan the first of the month following thirty days of service. Participants may contribute a portion of their salary, which is matched by the Company at 50%, not to be greater than 3% of eligible compensation, up to certain Internal Revenue Service limits. A Roth feature was added to the plan in 2016. All participants are 100% vested in all accounts at all times. Employer matching contributions for the years ended December 31, 2018, 2017 and 2016 were $1.4 million, $1.1 million and $1.0 million, respectively.

The profit sharing portion of the Plan is a defined contribution retirement plan. All profit sharing and discretionary contributions are completely discretionary. Participants are eligible for profit sharing contributions upon credit of 1,000 hours of service during the plan year, the attainment of 18 years of age, and employment on the last day of the year. Employees are vested in profit sharing contributions in the same manner as employer matching contributions discussed above. For the years ended December 31, 2018, 2017 and 2016, the Company made no employer profit sharing contributions.

(b) Employment Agreements

The Company has entered into contracts with certain senior officers that provide benefits under certain conditions following termination without cause, and/or following a change in control of the Company.

During 2012, the Company adopted a Deferred Compensation Plan, which provides its directors and select executive officers with the opportunity to defer current compensation. Under the Plan, participants are permitted to elect to defer compensation and the Company has the discretion to make additional contributions to the Plan on behalf of any participant based on a number of factors. Compensation expense under the Deferred Compensation Plan totaled $810,000, $652,000 and $540,000 for the years ended December 31, 2018, 2017 and 2016, respectively. The Company’s contributions totaled $583,000, $453,000 and $521,000 for the years ended December 31, 2018, 2017 and 2016, respectively. As of December 31, 2018 and 2017, the carrying value of the obligation related to the deferred compensation plans was $3.7 million and $2.8 million, respectively.

(d) Split-Dollar Life Insurance Benefit Plan

In conjunction with the Washington Banking Merger, the Company assumed the split-dollar life insurance benefit plan previously maintained by Washington Banking. Life insurance policies are maintained for current or former officers of the Bank or former Washington Banking officers that are subject to split-dollar life insurance agreements, which continue after the participant's employment and retirement. All participants are fully vested in their split-dollar life insurance benefits. The accrued benefit liability for the split-dollar life insurance agreements represents the present value of the future death benefits payable to the participants' beneficiaries.

The split-dollar life insurance projected benefit obligation is included in accrued expenses and other liabilities on the Company's Consolidated Statements of Financial Condition. As of December 31, 2018 and 2017, the carrying value of the obligation was $268,000 and $250,000, respectively.

(e) Salary Continuation Plan

In conjunction with the Premier Merger, the Company assumed an unfunded deferred compensation plan for select former Premier Commercial executive officers, some of which are current Heritage officers. Under the Salary Continuation Plan, the Company will pay each participant, or their beneficiary, specified benefits over specified periods beginning with the individual's termination of service due to retirement subject to early termination provisions. A liability is accrued for the obligation under this plan. As of December 31, 2018, the carrying value of the obligation was $4.6 million. The expense incurred for the Salary Continuation Plan was $184,000 during the year ended December 31, 2018. There was no expense incurred for the Salary Continuation Plan during the years ended December 31, 2017 and 2016.