Nature of Business and Significant Accounting Policies - Loans (Details)	12 Months Ended
	Jun. 30, 2017 USD ($)
Fair Quality
Allowance for loan losses
Possible realized loss term	4 years
Commercial | Term loans | Maximum
Allowance for loan losses
Loan term	10 years
Commercial | Lines of credit | Maximum
Allowance for loan losses
Loan term	1 year
Agricultural | Term loans | Maximum
Allowance for loan losses
Loan term	10 years
Agricultural | Lines of credit | Maximum
Allowance for loan losses
Loan term	1 year
Commercial and Agricultural
Allowance for loan losses
Maximum aggregate exposure not requiring a loan review within 12 months of most recent credit review	$ 250,000