Fair Value Measurements and Disclosures about Fair Value of Financial Instruments (Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Beginning balance	$ 380	$ 0
Unrealized gains recognized in earnings	658	0
Net settlements	(380)	0
Ending balance	$ 658	$ 0