Stock-Based Compensation - Nonvested Restricted Stock Shares Activity (Details) - Restricted Stock - First Financial Northwest, Inc. 2008 Equity Incentive Plan	3 Months Ended	9 Months Ended
	Sep. 30, 2024 $ / shares shares	Sep. 30, 2024 $ / shares shares
Shares
Nonvested Beginning Balance (in shares) | shares	7,673	27,618
Granted (in shares) | shares	0	7,673
Vested (in shares) | shares	0	(27,618)
Nonvested Ending Balance (in shares) | shares	7,673	7,673
Weighted-Average Grant Date Fair Value
Nonvested Beginning Balance, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 20.68	$ 14.92
Granted (in dollars per share) | $ / shares	0	20.68
Vested (in dollars per share) | $ / shares	0	14.92
Nonvested Ending Balance, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 20.68	$ 20.68
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	7,443	7,443
Weighted-Average Grant Date Fair Value
Nonvested Ending Balance, Weighted-Average Grant Date Fair Value (in dollars per share) | $ / shares	$ 20.68	$ 20.68
Forfeiture rate, percent	3.00%	3.00%