Stock-Based Compensation - Nonvested Restricted Stock Shares Activity (Details) - Restricted Stock - First Financial Northwest, Inc. 2008 Equity Incentive Plan	3 Months Ended
	Mar. 31, 2023 $ / shares shares
Shares
Nonvested Beginning Balance (in shares) | shares	31,272
Granted (in shares) | shares	27,618
Vested (in shares) | shares	(31,272)
Nonvested Ending Balance (in shares) | shares	27,618
Weighted-Average Grant Date Fair Value
Nonvested Beginning Balance, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 16.93
Granted (in dollars per share) | $ / shares	14.92
Vested (in dollars per share) | $ / shares	16.93
Nonvested Ending Balance, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 14.92
Vested and expected to vest assuming a 3% forfeiture rate over the vesting term
Shares
Expected to vest assuming a 3% forfeiture rate over the vesting term (in shares) | shares	26,789
Weighted-Average Grant Date Fair Value
Nonvested Ending Balance, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 14.92