Nature of Operations and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended
	Sep. 05, 2018	Sep. 30, 2019
Percent of outstanding common stock	55.00%
Common Stock, Shares, Issued	2,145,738,000	4,876,677,000
Common Stock, Par or Stated Value Per Share	$ 10.00	$ 0.01
Proceeds from Issuance of Common Stock	$ 21,500	$ 20,029
Charitable Foundation [Member]
Shares, Issued	48,767,000
Stock Issued During Period, Value, Other	$ 100,000
Common Stock [Member]
Employee Stock Ownership Plan (ESOP), Number of Allocated Shares	175,528,000
Employee Stock Ownership Plan (ESOP), Plan Description	1895 Bancorp of Wisconsin, Inc. was organized as a corporation under the laws of the United States and offered 45% of its common stock to be outstanding to the Bank’s eligible members, the ESOP, a community foundation and certain other persons.