The Fair Value Option For Certain Loans - Summary of the Fair Value Option (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of loans	$ (8,665)	$ (64,001)
Long-term loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of loans	(8,665)	(64,001)
Long-term loans | Noninterest Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of loans	$ (8,665)	$ (64,001)