Fair Value Measurements - Summary of Mortgage Loans Held-For-Sale, Fair Value Measurement (Details) - Fair value, measurements, nonrecurring - USD ($) $ in Thousands	Mar. 31, 2019	Sep. 30, 2018
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other repossessed property	$ 31,834	$ 22,225
Impaired loans	200,312	188,017
Loans held for sale, at lower of cost or fair value	3,648	5,456
Property held for sale	3,216	1,104
Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other repossessed property	0	0
Impaired loans	0	0
Loans held for sale, at lower of cost or fair value	0	0
Property held for sale	0	0
Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other repossessed property	0	0
Impaired loans	0	0
Loans held for sale, at lower of cost or fair value	3,648	5,456
Property held for sale	0	0
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other repossessed property	31,834	22,225
Impaired loans	200,312	188,017
Loans held for sale, at lower of cost or fair value	0	0
Property held for sale	$ 3,216	$ 1,104