Note 3 - Loans Receivable - Summary of Credit Quality Indicators (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Financing Receivable, Year One	$ 101,213		$ 101,213		$ 149,558
Financing Receivable, Year Two	132,811		132,811		178,872
Financing Receivable, Year Three	153,686		153,686		356,297
Financing Receivable, Year Four	403,697		403,697		187,203
Financing Receivable, Year Five	166,319		166,319		176,340
Financing Receivable Prior	456,059		456,059		317,405
Financing Receivable, Revolving	397,637		397,637		469,323
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	1,811,422		1,811,422		1,834,998
Current period gross write-offs, current			0		4
Current period gross write-offs, year one			200		1,029
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		259
Current period gross write-offs, year four			354		3,136
Current period gross write-offs, prior			303		141
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total	235	$ 1,907	857	$ 2,418	4,569
Pass [Member]
Financing Receivable, Year One	101,013		101,013		148,539
Financing Receivable, Year Two	132,311		132,311		136,962
Financing Receivable, Year Three	148,072		148,072		353,954
Financing Receivable, Year Four	358,966		358,966		163,488
Financing Receivable, Year Five	143,888		143,888		154,968
Financing Receivable Prior	417,694		417,694		296,291
Financing Receivable, Revolving	361,600		361,600		438,072
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	1,663,544		1,663,544		1,692,274
Criticized [Member]
Financing Receivable, Year One	200		200		500
Financing Receivable, Year Two	500		500		30,750
Financing Receivable, Year Three	4,500		4,500		393
Financing Receivable, Year Four	41,414		41,414		13,299
Financing Receivable, Year Five	11,703		11,703		19,706
Financing Receivable Prior	34,903		34,903		19,514
Financing Receivable, Revolving	0		0		1,138
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	93,220		93,220		85,300
Classified [Member]
Financing Receivable, Year One	0		0		519
Financing Receivable, Year Two	0		0		11,160
Financing Receivable, Year Three	1,114		1,114		1,950
Financing Receivable, Year Four	3,317		3,317		10,416
Financing Receivable, Year Five	10,728		10,728		1,666
Financing Receivable Prior	3,462		3,462		1,600
Financing Receivable, Revolving	36,037		36,037		30,113
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	54,658		54,658		57,424
Residential Portfolio Segment [Member]
Current period gross write-offs, total	200	(0)	200	132
Residential Portfolio Segment [Member] \| Single Family [Member]
Financing Receivable, Year One	16,377		16,377		19,139
Financing Receivable, Year Two	12,838		12,838		44,460
Financing Receivable, Year Three	37,676		37,676		18,196
Financing Receivable, Year Four	17,624		17,624		31,158
Financing Receivable, Year Five	33,901		33,901		34,256
Financing Receivable Prior	57,213		57,213		32,065
Financing Receivable, Revolving	23,459		23,459		25,083
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	199,088		199,088		204,357
Current period gross write-offs, current			0		0
Current period gross write-offs, year one			200		0
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		0
Current period gross write-offs, year four			0		0
Current period gross write-offs, prior			0		132
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total			200		132
Residential Portfolio Segment [Member] \| Single Family [Member] \| Pass [Member]
Financing Receivable, Year One	16,177		16,177		18,439
Financing Receivable, Year Two	12,338		12,338		44,460
Financing Receivable, Year Three	36,562		36,562		17,803
Financing Receivable, Year Four	16,256		16,256		26,055
Financing Receivable, Year Five	26,324		26,324		29,482
Financing Receivable Prior	55,231		55,231		32,065
Financing Receivable, Revolving	23,459		23,459		24,643
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	186,347		186,347		192,947
Residential Portfolio Segment [Member] \| Single Family [Member] \| Criticized [Member]
Financing Receivable, Year One	200		200		500
Financing Receivable, Year Two	500		500		0
Financing Receivable, Year Three	0		0		393
Financing Receivable, Year Four	0		0		1,596
Financing Receivable, Year Five	0		0		3,436
Financing Receivable Prior	0		0		0
Financing Receivable, Revolving	0		0		0
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	700		700		5,925
Residential Portfolio Segment [Member] \| Single Family [Member] \| Classified [Member]
Financing Receivable, Year One	0		0		200
Financing Receivable, Year Two	0		0		0
Financing Receivable, Year Three	1,114		1,114		0
Financing Receivable, Year Four	1,368		1,368		3,507
Financing Receivable, Year Five	7,577		7,577		1,338
Financing Receivable Prior	1,982		1,982		0
Financing Receivable, Revolving	0		0		440
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	12,041		12,041		5,485
Residential Portfolio Segment [Member] \| Multifamily [Member]
Financing Receivable, Year One	4,300		4,300		12,163
Financing Receivable, Year Two	20,055		20,055		31,564
Financing Receivable, Year Three	14,450		14,450		69,629
Financing Receivable, Year Four	61,163		61,163		39,593
Financing Receivable, Year Five	27,362		27,362		38,832
Financing Receivable Prior	60,902		60,902		42,713
Financing Receivable, Revolving	24,082		24,082		390
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	212,314		212,314		234,884
Current period gross write-offs, current			0		0
Current period gross write-offs, year one			0		0
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		0
Current period gross write-offs, year four			0		0
Current period gross write-offs, prior			0		0
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total			0		0
Residential Portfolio Segment [Member] \| Multifamily [Member] \| Pass [Member]
Financing Receivable, Year One	4,300		4,300		12,163
Financing Receivable, Year Two	20,055		20,055		5,314
Financing Receivable, Year Three	14,450		14,450		69,629
Financing Receivable, Year Four	48,196		48,196		24,693
Financing Receivable, Year Five	24,223		24,223		38,226
Financing Receivable Prior	60,323		60,323		23,199
Financing Receivable, Revolving	24,082		24,082		390
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	195,629		195,629		173,614
Residential Portfolio Segment [Member] \| Multifamily [Member] \| Criticized [Member]
Financing Receivable, Year One	0		0		0
Financing Receivable, Year Two	0		0		26,250
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	12,967		12,967		11,703
Financing Receivable, Year Five	0		0		606
Financing Receivable Prior	0		0		19,514
Financing Receivable, Revolving	0		0		0
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	12,967		12,967		58,073
Residential Portfolio Segment [Member] \| Multifamily [Member] \| Classified [Member]
Financing Receivable, Year One	0		0		0
Financing Receivable, Year Two	0		0		0
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	0		0		3,197
Financing Receivable, Year Five	3,139		3,139		0
Financing Receivable Prior	579		579		0
Financing Receivable, Revolving	0		0		0
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	3,718		3,718		3,197
Residential Portfolio Segment [Member] \| Farmland [Member]
Financing Receivable, Year One	0		0		106
Financing Receivable, Year Two	67		67		0
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	0		0		0
Financing Receivable, Year Five	0		0		0
Financing Receivable Prior	123		123		134
Financing Receivable, Revolving	0		0		0
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	190		190		240
Current period gross write-offs, current			0		0
Current period gross write-offs, year one			0		0
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		0
Current period gross write-offs, year four			0		0
Current period gross write-offs, prior			0		0
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total			0		0
Residential Portfolio Segment [Member] \| Farmland [Member] \| Pass [Member]
Financing Receivable, Year One	0		0		106
Financing Receivable, Year Two	67		67		0
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	0		0		0
Financing Receivable, Year Five	0		0		0
Financing Receivable Prior	123		123		134
Financing Receivable, Revolving	0		0		0
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	190		190		240
Commercial Real Estate Portfolio Segment [Member]
Current period gross write-offs, total	(0)	(0)	(0)	(0)
Commercial Real Estate Portfolio Segment [Member] \| Owner-occupied [Member]
Financing Receivable, Year One	54,866		54,866		35,483
Financing Receivable, Year Two	35,169		35,169		71,543
Financing Receivable, Year Three	84,852		84,852		81,427
Financing Receivable, Year Four	98,919		98,919		41,167
Financing Receivable, Year Five	35,308		35,308		38,446
Financing Receivable Prior	108,268		108,268		79,425
Financing Receivable, Revolving	4,800		4,800		24,921
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	422,182		422,182		372,412
Current period gross write-offs, current			0		0
Current period gross write-offs, year one			0		0
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		0
Current period gross write-offs, year four			0		0
Current period gross write-offs, prior			0		0
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total			0		0
Commercial Real Estate Portfolio Segment [Member] \| Owner-occupied [Member] \| Pass [Member]
Financing Receivable, Year One	54,866		54,866		35,483
Financing Receivable, Year Two	35,169		35,169		67,043
Financing Receivable, Year Three	80,352		80,352		81,427
Financing Receivable, Year Four	98,919		98,919		41,167
Financing Receivable, Year Five	35,308		35,308		38,446
Financing Receivable Prior	108,268		108,268		79,425
Financing Receivable, Revolving	4,545		4,545		24,921
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	417,427		417,427		367,912
Commercial Real Estate Portfolio Segment [Member] \| Owner-occupied [Member] \| Criticized [Member]
Financing Receivable, Year One	0		0		0
Financing Receivable, Year Two	0		0		4,500
Financing Receivable, Year Three	4,500		4,500		0
Financing Receivable, Year Four	0		0		0
Financing Receivable, Year Five	0		0		0
Financing Receivable Prior	0		0		0
Financing Receivable, Revolving	0		0		0
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	4,500		4,500		4,500
Commercial Real Estate Portfolio Segment [Member] \| Owner-occupied [Member] \| Classified [Member]
Financing Receivable, Year One	0		0		0
Financing Receivable, Year Two	0		0		0
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	0		0		0
Financing Receivable, Year Five	0		0		0
Financing Receivable Prior	0		0		0
Financing Receivable, Revolving	255		255		0
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	255		255		0
Commercial Real Estate Portfolio Segment [Member] \| Non-owner Occupied [Member]
Financing Receivable, Year One	4,088		4,088		46,243
Financing Receivable, Year Two	42,060		42,060		18,709
Financing Receivable, Year Three	7,119		7,119		154,994
Financing Receivable, Year Four	206,226		206,226		58,931
Financing Receivable, Year Five	64,213		64,213		62,049
Financing Receivable Prior	220,954		220,954		152,963
Financing Receivable, Revolving	14,249		14,249		31,903
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	558,909		558,909		525,792
Current period gross write-offs, current			0		0
Current period gross write-offs, year one			0		740
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		0
Current period gross write-offs, year four			0		0
Current period gross write-offs, prior			0		0
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total			0		740
Commercial Real Estate Portfolio Segment [Member] \| Non-owner Occupied [Member] \| Pass [Member]
Financing Receivable, Year One	4,088		4,088		46,243
Financing Receivable, Year Two	42,060		42,060		7,549
Financing Receivable, Year Three	7,119		7,119		154,994
Financing Receivable, Year Four	177,779		177,779		58,931
Financing Receivable, Year Five	52,510		52,510		46,057
Financing Receivable Prior	185,736		185,736		152,963
Financing Receivable, Revolving	14,249		14,249		31,903
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	483,541		483,541		498,640
Commercial Real Estate Portfolio Segment [Member] \| Non-owner Occupied [Member] \| Criticized [Member]
Financing Receivable, Year One	0		0		0
Financing Receivable, Year Two	0		0		0
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	28,447		28,447		0
Financing Receivable, Year Five	11,703		11,703		15,664
Financing Receivable Prior	34,903		34,903		0
Financing Receivable, Revolving	0		0		0
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	75,053		75,053		15,664
Commercial Real Estate Portfolio Segment [Member] \| Non-owner Occupied [Member] \| Classified [Member]
Financing Receivable, Year One	0		0		0
Financing Receivable, Year Two	0		0		11,160
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	0		0		0
Financing Receivable, Year Five	0		0		328
Financing Receivable Prior	315		315		0
Financing Receivable, Revolving	0		0		0
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	315		315		11,488
Construction [Member] \| Construction and Land Development [Member]
Financing Receivable, Year One	539		539		3,149
Financing Receivable, Year Two	647		647		5,358
Financing Receivable, Year Three	3,212		3,212		21,630
Financing Receivable, Year Four	13,663		13,663		8,849
Financing Receivable, Year Five	476		476		718
Financing Receivable Prior	96		96		234
Financing Receivable, Revolving	293,685		293,685		353,447
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	312,318		312,318		393,385
Current period gross write-offs, current			0		0
Current period gross write-offs, year one			0		289
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		259
Current period gross write-offs, year four			35		3,136
Current period gross write-offs, prior			0		0
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total			35		3,684
Construction [Member] \| Construction and Land Development [Member] \| Pass [Member]
Financing Receivable, Year One	539		539		3,149
Financing Receivable, Year Two	647		647		5,358
Financing Receivable, Year Three	3,212		3,212		19,680
Financing Receivable, Year Four	11,714		11,714		8,849
Financing Receivable, Year Five	476		476		718
Financing Receivable Prior	96		96		234
Financing Receivable, Revolving	261,289		261,289		325,885
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	277,973		277,973		363,873
Construction [Member] \| Construction and Land Development [Member] \| Criticized [Member]
Financing Receivable, Year One					0
Financing Receivable, Year Two					0
Financing Receivable, Year Three					0
Financing Receivable, Year Four					0
Financing Receivable, Year Five					0
Financing Receivable Prior					0
Financing Receivable, Revolving					1,138
Financing Receivable, revolving converted to term					0
Collateral dependent loans					1,138
Construction [Member] \| Construction and Land Development [Member] \| Classified [Member]
Financing Receivable, Year One	0		0		0
Financing Receivable, Year Two	0		0		0
Financing Receivable, Year Three	0		0		1,950
Financing Receivable, Year Four	1,949		1,949		0
Financing Receivable, Year Five	0		0		0
Financing Receivable Prior	0		0		0
Financing Receivable, Revolving	32,396		32,396		26,424
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	34,345		34,345		28,374
Commercial Portfolio Segment [Member]
Current period gross write-offs, total	(0)	4	622	4
Commercial Portfolio Segment [Member] \| Commercial and Industrial [Member]
Financing Receivable, Year One	20,912		20,912		33,088
Financing Receivable, Year Two	21,820		21,820		7,197
Financing Receivable, Year Three	6,345		6,345		10,237
Financing Receivable, Year Four	5,977		5,977		7,505
Financing Receivable, Year Five	5,059		5,059		2,026
Financing Receivable Prior	8,256		8,256		9,150
Financing Receivable, Revolving	36,848		36,848		33,151
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	105,217		105,217		102,354
Current period gross write-offs, current			0		4
Current period gross write-offs, year one			0		0
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		0
Current period gross write-offs, year four			319		0
Current period gross write-offs, prior			303		0
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total			622		4
Commercial Portfolio Segment [Member] \| Commercial and Industrial [Member] \| Pass [Member]
Financing Receivable, Year One	20,912		20,912		32,769
Financing Receivable, Year Two	21,820		21,820		7,197
Financing Receivable, Year Three	6,345		6,345		10,237
Financing Receivable, Year Four	5,977		5,977		3,793
Financing Receivable, Year Five	5,047		5,047		2,026
Financing Receivable Prior	7,670		7,670		7,550
Financing Receivable, Revolving	33,462		33,462		29,902
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	101,233		101,233		93,474
Commercial Portfolio Segment [Member] \| Commercial and Industrial [Member] \| Classified [Member]
Financing Receivable, Year One	0		0		319
Financing Receivable, Year Two	0		0		0
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	0		0		3,712
Financing Receivable, Year Five	12		12		0
Financing Receivable Prior	586		586		1,600
Financing Receivable, Revolving	3,386		3,386		3,249
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	3,984		3,984		8,880
Consumer Portfolio Segment [Member]
Current period gross write-offs, total	(0)	$ (0)	(0)	$ 9
Consumer Portfolio Segment [Member] \| Unsecured [Member]
Financing Receivable, Year One	0		0		0
Financing Receivable, Year Two	0		0		0
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	0		0		0
Financing Receivable, Year Five	0		0		0
Financing Receivable Prior	0		0		0
Financing Receivable, Revolving	168		168		343
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	168		168		343
Current period gross write-offs, current			0		0
Current period gross write-offs, year one			0		0
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		0
Current period gross write-offs, year four			0		0
Current period gross write-offs, prior			0		0
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total			0		0
Consumer Portfolio Segment [Member] \| Unsecured [Member] \| Pass [Member]
Financing Receivable, Year One	0		0		0
Financing Receivable, Year Two	0		0		0
Financing Receivable, Year Three	0		0		0
Financing Receivable, Year Four	0		0		0
Financing Receivable, Year Five	0		0		0
Financing Receivable Prior	0		0		0
Financing Receivable, Revolving	168		168		343
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	168		168		343
Consumer Portfolio Segment [Member] \| Secured [Member]
Financing Receivable, Year One	131		131		187
Financing Receivable, Year Two	155		155		41
Financing Receivable, Year Three	32		32		184
Financing Receivable, Year Four	125		125		0
Financing Receivable, Year Five	0		0		13
Financing Receivable Prior	247		247		721
Financing Receivable, Revolving	346		346		85
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	1,036		1,036		1,231
Current period gross write-offs, current			0		0
Current period gross write-offs, year one			0		0
Current period gross write-offs, year two			0		0
Current period gross write-offs, year three			0		0
Current period gross write-offs, year four			0		0
Current period gross write-offs, prior			0		9
Current period gross write-offs, revolving			0		0
Current period gross write-offs, revolving converted to term			0		0
Current period gross write-offs, total			0		9
Consumer Portfolio Segment [Member] \| Secured [Member] \| Pass [Member]
Financing Receivable, Year One	131		131		187
Financing Receivable, Year Two	155		155		41
Financing Receivable, Year Three	32		32		184
Financing Receivable, Year Four	125		125		0
Financing Receivable, Year Five	0		0		13
Financing Receivable Prior	247		247		721
Financing Receivable, Revolving	346		346		85
Financing Receivable, revolving converted to term	0		0		0
Collateral dependent loans	$ 1,036		$ 1,036		$ 1,231

MainStreet Bancshares, Inc. 10-Q