Fair Value Measurements - Summary of Valuation Techniques and Significant Unobservable Inputs Used to Measure Level 3 Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Property held for sale	$ 705	$ 2,757
Fair value, measurements, nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other repossessed property	17,348	34,721
Impaired loans	591,541	413,644
Fair value, measurements, nonrecurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other repossessed property	17,348	34,721
Impaired loans	591,541	$ 413,644
Property held for sale	$ 705