Note 11 - Fair Value Measurement - Carrying Values and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Investment securities available for sale	$ 303,515	$ 340,344
Accrued interest receivable	8,305	8,159
Sold loan servicing rights	3,220	3,281
Reported Value Measurement [Member]
Cash and cash equivalents	87,863	72,448
Investment securities available for sale	303,515	340,344
Loans held for sale	1,557	472
Loans receivable, net	1,647,217	1,675,186
FHLB stock	14,906	14,435
Accrued interest receivable	8,305	8,159
Sold loan servicing rights	3,220	3,281
FHLB Borrowings	300,000	290,000
Line of Credit	9,500	6,500
Subordinated debt, net	34,608	39,514
Accrued interest payable	1,514	3,295
Interest rate swap derivative	1,684	267
Interest rate swap derivative		123
Reported Value Measurement [Member] \| Demand Deposits [Member]
Deposits	1,097,215	1,040,184
Reported Value Measurement [Member] \| Time Deposits [Member]
Deposits	557,421	647,842
Estimate of Fair Value Measurement [Member]
Cash and cash equivalents	87,863	72,448
Investment securities available for sale	303,515	340,344
Loans held for sale	1,557	472
Loans receivable, net	1,526,496	1,536,748
FHLB stock	14,906	14,435
Accrued interest receivable	8,305	8,159
Sold loan servicing rights	3,220	3,281
FHLB Borrowings	299,865	288,512
Line of Credit	9,537	6,526
Subordinated debt, net	36,379	39,974
Accrued interest payable	1,514	3,295
Interest rate swap derivative	1,684	267
Interest rate swap derivative		123
Estimate of Fair Value Measurement [Member] \| Demand Deposits [Member]
Deposits	1,097,215	1,040,184
Estimate of Fair Value Measurement [Member] \| Time Deposits [Member]
Deposits	556,473	648,232
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member]
Cash and cash equivalents	87,863	72,448
Investment securities available for sale	13,109	13,976
Loans held for sale	0	0
Loans receivable, net	0	0
FHLB stock	0	0
Accrued interest receivable	0	0
Sold loan servicing rights	0	0
FHLB Borrowings	0	0
Line of Credit	0	0
Subordinated debt, net	0	0
Accrued interest payable	0	0
Interest rate swap derivative	0	0
Interest rate swap derivative		0
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| Demand Deposits [Member]
Deposits	1,097,215	1,040,184
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 1 [Member] \| Time Deposits [Member]
Deposits	0	0
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member]
Cash and cash equivalents	0	0
Investment securities available for sale	277,208	294,487
Loans held for sale	1,557	472
Loans receivable, net	0	0
FHLB stock	14,906	14,435
Accrued interest receivable	8,305	8,159
Sold loan servicing rights	0	0
FHLB Borrowings	0	0
Line of Credit	0	0
Subordinated debt, net	0	0
Accrued interest payable	1,514	3,295
Interest rate swap derivative	1,684	267
Interest rate swap derivative		123
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Demand Deposits [Member]
Deposits	0	0
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 2 [Member] \| Time Deposits [Member]
Deposits	0	0
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member]
Cash and cash equivalents	0	0
Investment securities available for sale	13,198	31,881
Loans held for sale	0	0
Loans receivable, net	1,526,496	1,536,748
FHLB stock	0	0
Accrued interest receivable	0	0
Sold loan servicing rights	3,220	3,281
FHLB Borrowings	299,865	288,512
Line of Credit	9,537	6,526
Subordinated debt, net	36,379	39,974
Accrued interest payable	0	0
Interest rate swap derivative	0	0
Interest rate swap derivative		0
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member] \| Demand Deposits [Member]
Deposits	0	0
Estimate of Fair Value Measurement [Member] \| Fair Value, Inputs, Level 3 [Member] \| Time Deposits [Member]
Deposits	$ 556,473	$ 648,232

First Northwest Bancorp 10-Q