Fair Value Measurements - Fair value on a recurring basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Jun. 30, 2020
State and political subdivisions
Fair value measurement, recurring basis	$ 43,292	$ 41,988
Other securities
Fair value measurement, recurring basis	20,837	7,624
Mortgage-backed securities
Fair value measurement, recurring basis	126,280	126,912
Fair Value, Inputs, Level 1 | State and political subdivisions
Fair value measurement, recurring basis	0	0
Fair Value, Inputs, Level 1 | Other securities
Fair value measurement, recurring basis	0	0
Fair Value, Inputs, Level 1 | Mortgage-backed securities
Fair value measurement, recurring basis	0	0
Fair Value, Inputs, Level 2 | State and political subdivisions
Fair value measurement, recurring basis	43,292	41,988
Fair Value, Inputs, Level 2 | Other securities
Fair value measurement, recurring basis	20,837	7,624
Fair Value, Inputs, Level 2 | Mortgage-backed securities
Fair value measurement, recurring basis	126,280	126,912
Fair Value, Inputs, Level 3 | State and political subdivisions
Fair value measurement, recurring basis	0	0
Fair Value, Inputs, Level 3 | Other securities
Fair value measurement, recurring basis	0	0
Fair Value, Inputs, Level 3 | Mortgage-backed securities
Fair value measurement, recurring basis	$ 0	$ 0