Heritage Financial Corporation (Parent Only) (Condensed Income Statement) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Income Statements, Captions [Line Items]
ESOP loan									$ 110,437	$ 67,630	$ 65,588
Total interest income	38,439	35,031	30,023	17,613	18,552	18,533	16,859	17,484	121,106	71,428	69,109
Junior subordinated debentures									458	0	0
Total interest expense	1,659	1,724	1,426	872	907	952	919	946	5,681	3,724	4,534
Net interest income	36,780	33,307	28,597	16,741	17,645	17,581	15,940	16,538	115,425	67,704	64,575
Other income									4,986	2,493	1,809
Total noninterest income	3,897	5,483	4,780	2,307	2,430	2,582	2,357	2,282	16,467	9,651	7,272
Professional services									6,185	3,936	2,543
Other expense									9,112	4,798	4,343
Total noninterest expense	29,243	28,363	26,994	14,779	18,504	14,285	13,007	13,719	99,379	59,515	50,392
Income before income taxes	8,583	9,833	5,692	3,811	1,143	4,800	3,982	4,243	27,919	14,168	19,439
Income tax benefit	1,328	2,765	1,544	1,268	433	1,510	1,292	1,358	6,905	4,593	6,178
Net income	7,255	7,068	4,148	2,543	710	3,290	2,690	2,885	21,014	9,575	13,261
Parent Company
Condensed Income Statements, Captions [Line Items]
Interest earning deposits and other assets									17	22	44
ESOP loan									0	0	8
Total interest income									17	22	52
Junior subordinated debentures									458	0	0
Total interest expense									458	0	0
Net interest income									(441)	22	52
Dividends from subsidiary banks									66,300	26,000	14,100
Equity in (excess distributed) undistributed income of subsidiary banks									(40,737)	(13,001)	962
Other income									3	0	0
Total noninterest income									25,566	12,999	15,062
Professional services									2,943	1,718	0
Other expense									3,109	2,905	2,766
Total noninterest expense									6,052	4,623	2,766
Income before income taxes									19,073	8,398	12,348
Income tax benefit									(1,941)	(1,177)	(913)
Net income									$ 21,014	$ 9,575	$ 13,261