Fair Value Measurements - Qualitative Valuation (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Real estate owned	$ 959	$ 393
Real estate owned | Appraised Value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount for cost to sell	6.00%	6.00%
Loans measured for impairment based on the fair value of the underlying collateral | Minimum | Appraised Value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount for cost to sell	6.00%	6.00%
Loans measured for impairment based on the fair value of the underlying collateral | Maximum | Appraised Value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount for cost to sell	8.00%	8.00%