Employee Benefits (Details) (USD $)	0 Months Ended	8 Months Ended	12 Months Ended
	May 01, 2014	Dec. 31, 2014	Dec. 31, 2014 Plans	Dec. 31, 2013	Dec. 31, 2012
Employee Benefits [Line Items]
Number of retirement plans			3
Percentage of employer contribution fully vested	100.00%	100.00%
Heritage Financial Corporation 401(k) Plan and Trust
Employee Benefits [Line Items]
Required contribution percentage			1.50%
Minimum hours of service required for eligibility			1,000
Minimum age required for eligibility			18 years
Employer profit sharing contributions			475,000
KSOP Defined Contribution Plan
Employee Benefits [Line Items]
Required contribution percentage				3.00%	3.00%
Participant's eligible compensation, percentage				2.00%	2.00%
Years until employer contribution is fully vested under ratable method			6 years
Employer profit sharing contributions				600,000	631,000
Heritage Financial Corporation 401(k) Plan and Trust Salary Saving Plan
Employee Benefits [Line Items]
Minimum age required for eligibility			18 years
Minimum service days required for eligibility			30 days
Employer matching contribution, percentage of employees' gross pay			50.00%
Maximum annual contributions per employee, percentage			3.00%
Employer matching contribution amount			852,000
KSOP Salary Saving Plan
Employee Benefits [Line Items]
Employer matching contribution amount				497,000	444,000
KSOP Employee Stock Ownership Plan
Employee Benefits [Line Items]
Minimum age required for eligibility					18 years
Minimum service years required for eligibility					1 year
ESOP, compensation expense			0	0	139,000
ESOP, number of committed-to-be-released shares		0	0	0
ESOP, number of suspense shares		0	0
Deferred Compensation Plan
Employee Benefits [Line Items]
Deferred compensation plan, compensation expense			343,000	445,000	312,000
Deferred compensation plan, employer contributions			414,000	155,000	150,000
Accrued Expenses and Other Liabilities [Member] | Washington Banking
Employee Benefits [Line Items]
Split-dollar life insurance benefits obligation		1,200,000	1,200,000	$ 0