Loans Receivable and Allowance for Loan Losses: Significant Concentrations of Credit Risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Receivables [Abstract]
Loans secured by real estate	$ 774,227
Undisbursed portion of construction loans in process	$ 83,237	$ 82,411
Loans secured by real estate, percentage of total portfolio (as a percent)	94.30%
Concentration of credit risk, real estate loans by industry, benchmark percentage (as a percent)	20.00%
Ratio of loans to appraisal or purchase price (as a percent)	90.00%