Loans - Summary of Internal Risk Ratings of Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	$ 329,994	$ 331,598
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	184,400	189,291
Commercial Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	1,475	1,492
Commercial Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	43,915	46,184
Internal Credit Risk Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	229,790	236,967
Internal Credit Risk Rating [Member] \| Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	184,400	189,291
Internal Credit Risk Rating [Member] \| Commercial Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	1,475	1,492
Internal Credit Risk Rating [Member] \| Commercial Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	43,915	46,184
Pass [Member] \| Internal Credit Risk Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	196,703	201,636
Pass [Member] \| Internal Credit Risk Rating [Member] \| Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	160,045	163,961
Pass [Member] \| Internal Credit Risk Rating [Member] \| Commercial Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	36,658	37,675
Watch and Special Mention [Member] \| Internal Credit Risk Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	23,272	24,977
Watch and Special Mention [Member] \| Internal Credit Risk Rating [Member] \| Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	17,985	19,272
Watch and Special Mention [Member] \| Internal Credit Risk Rating [Member] \| Commercial Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	5,287	5,705
Substandard [Member] \| Internal Credit Risk Rating [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	9,815	10,354
Substandard [Member] \| Internal Credit Risk Rating [Member] \| Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	6,370	6,058
Substandard [Member] \| Internal Credit Risk Rating [Member] \| Commercial Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	1,475	1,492
Substandard [Member] \| Internal Credit Risk Rating [Member] \| Commercial Other [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases receivable gross carrying amount	$ 1,970	$ 2,804

1895 Bancorp of Wisconsin, Inc. 10-Q