Derivative Financial Instruments - Summary of Offsetting Assets and Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative financial assets, gross amount	$ 1,626	$ 525
Derivative financial liabilities, gross amount	(19,914)	(81,974)
Derivative financial assets (liabilities), gross amount	(18,288)	(81,449)
Derivative financial assets, amount offset	(1,626)	(525)
Derivative financial liabilities, amount offset	1,626	525
Derivative financial assets (liabilities), Net, amount offset	0	0
Derivative financial assets, net amount presented in Consolidated Balance Sheets	0	0
Derivative financial liabilities, net amount presented in Consolidated Balance Sheets	(18,288)	(81,449)
Derivative financial assets (liabilities), net amount presented in Consolidated Balance Sheets	(18,288)	(81,449)
Derivative financial assets, Held/pledged financial instruments	0	0
Derivative financial liabilities, Held/pledged financial instruments	18,288	81,449
Derivative liabilities (assets), Net, Held/pledged financial instruments	18,288	81,449
Derivative financial asset, net amount	0	0
Derivative financial liabilities, net amount	0	0
Derivative financial assets (liabilities), net, amount offset against collateral	$ 0	$ 0