FHLB Advances and Other Borrowings - Schedule of Advances, Related Party Notes (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Other	$ 700	$ 0
Total	471,700	871,000
Fair value adjustment	19	37
Total FHLB advances and other borrowings	471,719	871,037
Notes payable to banks
Debt Instrument [Line Items]
Federal Home Loan Bank (FHLB) notes payable and fed funds advance	$ 431,000	640,000
Notes payable to banks | Minimum
Debt Instrument [Line Items]
Stated interest rate (as a percent)	1.05%
Notes payable to banks | Maximum
Debt Instrument [Line Items]
Stated interest rate (as a percent)	3.66%
Federal Home Loan Bank fed funds advance
Debt Instrument [Line Items]
Interest rate (as a percent)	1.32%
Federal Home Loan Bank (FHLB) notes payable and fed funds advance	$ 40,000	$ 231,000