Net Income (Loss) Per Share (Additional Information) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss)	$ 77,332	$ (164,053)	$ 96,422	$ (110,825)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	(20,749)	(167,141)	(3,050)	(119,676)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ 98,081	$ 3,088	$ 99,472	$ 8,851
Weighted Average Number of Shares Outstanding, Basic	285,866	294,103	286,849	292,720
Dilutive Securities, Effect on Basic Earnings Per Share	0	0	0	0
Weighted Average Number of Shares Outstanding, Diluted	285,866	294,103	286,849	292,720
Earnings Per Share, Basic	$ 0.27	$ (0.56)	$ 0.34	$ (0.38)
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic Share	0.34	0.01	0.35	0.03
Income (Loss) from Continuing Operations, Per Basic Share	$ (0.07)	$ (0.57)	$ (0.01)	$ (0.41)
Weighted Average Number of Shares, Contingently Issuable	2,646	2,836	2,422	2,387
Income (Loss) from Continuing Operations, Per Diluted Share	$ (0.07)	$ (0.57)	$ (0.01)	$ (0.41)
Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Diluted Share	0.34	0.01	0.35	0.03
Earnings Per Share, Diluted	$ 0.27	$ (0.56)	$ 0.34	$ (0.38)
Anti-dilutive common equivalent shares excluded from computation of diluted net income (loss) per share	460	2,679	635	4,178