Fair Value Measurements - Summary of Mortgage Loans Held-For-Sale, Fair Value Measurement (Details) - Fair value, measurements, nonrecurring - USD ($) $ in Thousands	Mar. 31, 2020	Sep. 30, 2019
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other repossessed property	$ 21,486	$ 34,721
Impaired loans	559,155	413,644
Mortgage loans held for sale, at lower of cost or fair value	4,342	7,351
Property held for sale	706	2,757
Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other repossessed property	0	0
Impaired loans	0	0
Mortgage 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
Mortgage loans held for sale, at lower of cost or fair value	4,342	7,351
Property held for sale	0	0
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other repossessed property	21,486	34,721
Impaired loans	559,155	413,644
Mortgage loans held for sale, at lower of cost or fair value	0	0
Property held for sale	$ 706	$ 2,757