FIRST FINANCIAL NORTHWEST, INC. AND SUBSIDIARIES CONSOLIDATED STATEMETNS OF STOCKHOLDERS' EQUITY (PARENTHETICALS) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Cash dividend declared and paid per share (usd per share)	$ 0.0031	$ 0.0027	$ 0.0024
Allocated shares	112,853	112,854	112,853

Number of shares of capital stock issued (purchased by employees) in connection with an employee stock ownership plan.

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Balance Type:	na
Period Type:	duration