Quarterly Data Derived from Unaudited Consolidated Financial Statements with All Recurring Adjustments (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2017
Effect of Fourth Quarter Events [Line Items]
Revenues	$ 470,658	$ 449,197	$ 409,583	$ 493,654	$ 479,432	$ 449,449	$ 466,193	$ 447,224	$ 1,823,092	[1]	$ 1,842,298	[1]	$ 1,728,175	[1]
Gross Profit	276,459	258,506	227,992	280,216	280,634	248,118	249,173	238,986	1,043,173		1,016,911		924,337
Net income (loss)	$ 108,129	$ 9,259	$ (20,749)	$ 17,699	$ (44,508)	$ (20,720)	$ (167,141)	$ 47,465	213,810		(159,928)		(150,996)
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent									$ 114,338		$ (184,904)		$ (178,341)
Net income (loss) per share:
Basic (per share)	$ 0.38	$ 0.03	$ (0.07)	$ 0.06	$ (0.16)	$ (0.07)	$ (0.57)	$ 0.16	$ 0.75		$ (0.55)		$ (0.52)
Income (Loss) from Continuing Operations, Per Basic Share									0.40		(0.63)		(0.62)
Diluted (per share)	$ 0.37	$ 0.03	$ (0.07)	$ 0.06	$ (0.16)	$ (0.07)	$ (0.57)	$ 0.16	0.74		(0.55)		(0.52)
Income (Loss) from Continuing Operations, Per Diluted Share									$ 0.39		$ (0.63)		$ (0.62)
Weighted Average Number of Shares Outstanding:
Basic (in shares)	285,754	285,942	285,866	287,796	287,052	292,663	294,103	291,367	286,347		291,318		289,348
Diluted (in shares)	291,598	288,648	285,866	292,359	287,052	292,663	294,103	295,995	290,125		291,318		289,348

[1] Segment revenues differ from reported revenues due to certain revenue adjustments related to acquisitions that would otherwise have been recognized but for the purchase accounting treatment of the business combinations. These revenues are included to allow for more complete comparisons to the financial results of historical operations and in evaluating management performance.