Current and Deferred Income Tax (Benefit) and Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Deferred Income Tax Assets And Liabilities
Income (loss) before income taxes	$ (11,421)	$ (21,766)	$ 100,032	$ 76,368
Current tax (benefit) expense	(5,803)	(5,764)	(6,564)	27,270
Deferred tax expense (benefit)	2,354	(2,670)	40,844	4,451
Deferred tax expense (benefit) - impact of tax reform	33		(11,203)
Total deferred tax expense (benefit)	2,387	(2,670)	29,641	4,451
Total tax expense (benefit)	$ (3,416)	$ (8,434)	$ 23,077	$ 31,721