Heritage Financial Corporation (Parent Only) (Condensed Cash Flow Statement) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Cash Flow Statements, Captions [Line Items]
Net income	$ 21,014	$ 9,575	$ 13,261
Tax (benefit) provision realized from stock options exercised, share-based payment and dividends on unallocated ESOP shares	(112)	13	93
Recognition of compensation related to ESOP shares and share based payment	1,395	1,223	1,185
Stock option compensation expense	20	71	106
Net cash provided by operating activities	51,336	30,897	27,882
Net cash used in investing activities	(121,649)	(16,593)	(3,502)
Common stock cash dividends paid	(12,892)	(6,672)	(12,155)
Proceeds from exercise of stock options	921	176	129
Tax benefit (provision) realized from stock options exercised, share-based payment and dividends on unallocated ESOP shares	112	(13)	(93)
Repurchase of common stock	(2,601)	(8,825)	(6,023)
Net cash provided by (used in) financing activities	61,549	11,828	(43,285)
Net (decrease) increase in cash and cash equivalents	(8,764)	26,132	(18,905)
Cash and cash equivalents at beginning of year	130,400	104,268	123,173
Cash and cash equivalents at end of year	121,636	130,400	104,268
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Net income	21,014	9,575	13,261
Equity in excess distributed (undistributed) income of subsidiary bank	40,737	13,001	(962)
Tax (benefit) provision realized from stock options exercised, share-based payment and dividends on unallocated ESOP shares	(112)	13	93
Recognition of compensation related to ESOP shares and share based payment	1,395	1,223	1,185
Stock option compensation expense	20	71	106
Net change in other assets and liabilities	811	(489)	7
Net cash provided by operating activities	63,865	23,394	13,690
ESOP loan principal repayments	0	0	161
Investment in subsidiary	(43,215)	(21,666)	0
Net cash used in investing activities	(43,215)	(21,666)	161
Common stock cash dividends paid	(12,892)	(6,672)	(12,155)
Proceeds from exercise of stock options	921	176	129
Tax benefit (provision) realized from stock options exercised, share-based payment and dividends on unallocated ESOP shares	112	(13)	(93)
Repurchase of common stock	(2,601)	(8,825)	(6,023)
Net cash provided by (used in) financing activities	(14,460)	(15,334)	(18,142)
Net (decrease) increase in cash and cash equivalents	6,190	(13,606)	(4,291)
Cash and cash equivalents at beginning of year	2,645	16,251	20,542
Cash and cash equivalents at end of year	$ 8,835	$ 2,645	$ 16,251