Summary of Significant Accounting Policies - Significant events (Details)	6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2021 USD ($) loan	Dec. 31, 2020 USD ($) loan	Mar. 24, 2021 loan	Jun. 30, 2021 USD ($) item loan	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)
Financing Receivable, Impaired [Line Items]
Number of loans modification request received | loan	88			88
Aggregate value of requested loans to be modified	$ 22,900,000			$ 22,900,000
Modified loans requested and performing under Cares Act	22,800,000			$ 22,800,000
Percentage of performing loans				99.50%
TDR granted during period, including loans transferred out of TDR status | loan				3
TDR investment modified during period, including loans transferred out of TDR status				$ 294,000
TDR granted and subsequently transferred out of TDR status during the period | loan				1
Consecutive monthly payments after the end of the deferral period | item				6
Allowance for loan losses	$ 1,412,489			$ 1,412,489	$ 1,353,427	$ 1,293,965
PPP
Financing Receivable, Impaired [Line Items]
Deferment payment period				6 months
Number of loan originated | loan	9	17
Value of loan	$ 729,000	$ 1,100,000
Processing fee income	$ 32,000	$ 44,000
Number of loans forgiven | loan	1		17
Amount of loan forgiveness	$ 3,000			$ 3,000