The Fair Value Option For Certain Loans - Summary of the Fair Value Option (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of loans	$ 6,060	$ 14,198	$ (63,158)	$ 35,253
Long-term loans and written loan commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of loans	6,060	14,198	(63,158)	35,253
Long-term loans and written loan commitments | Noninterest Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of loans	$ 6,060	$ 14,198	$ (63,158)	$ 35,253