Income Taxes (Additional Information) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Acquisition [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	24.53%	21.00%	24.53%
Deferred Income Tax Expense (Benefit)			$ (18,975)	$ (90,836)
Effective Income Tax Rate Reconciliation, Percent	45.70%	(85.60%)	55.70%	32.40%
TCJA [Domain]
Business Acquisition [Line Items]
Deferred Income Tax Expense (Benefit)				$ 87,000
Current Income Tax Expense (Benefit)				$ 2,000