Supplemental Guarantor Information - Condensed Consolidating Statements of Cash Flows (Detail) - USD ($) $ in Thousands		6 Months Ended
	Jan. 02, 2018	Mar. 31, 2019	Mar. 31, 2018
Net cash provided by (used in) operating activities		$ (242,144)	$ 39,966
Investing Activities
Purchases of property and equipment		(26,320)	(24,833)
Acquisition of businesses, net		(163,973)	(2,726,561)
Proceeds from the sale of assets		1,428	413
Intercompany activity		0	0
Net cash provided by (used in) investing activities		(188,865)	(2,750,981)
Financing Activities
Borrowings under revolving lines of credit		1,880,684	1,530,667
Repayments under revolving lines of credit		(1,557,615)	(1,097,463)
Borrowings under term loan		0	970,000
Repayments under term loan		(4,850)	(441,000)
Borrowings under senior notes		0	1,300,000
Payment of debt issuance costs	$ (65,300)	0	(67,723)
Repayments under equipment financing facilities and other		(2,642)	(5,643)
Proceeds from issuance of convertible preferred stock		0	400,000
Payment of stock issuance costs		0	(1,279)
Payment of dividends on preferred stock		(12,000)	(978)
Proceeds from issuance of common stock related to equity awards		1,559	5,317
Taxes paid related to net share settlement of equity awards		(3,617)	(3,933)
Intercompany activity		0	0
Net cash provided by (used in) financing activities		301,519	2,587,965
Effect of exchange rate changes on cash and cash equivalents		208	800
Net increase (decrease) in cash and cash equivalents		(129,282)	(122,250)
Cash and cash equivalents, beginning of period		129,927	138,250
Cash and cash equivalents, end of period		645	16,000
Reportable Legal Entities [Member] | Parent Company [Member]
Net cash provided by (used in) operating activities		(62,741)	(47,488)
Investing Activities
Purchases of property and equipment		(2,781)	(5,050)
Acquisition of businesses, net		0	(2,726,561)
Proceeds from the sale of assets		0	0
Intercompany activity		84,430	606,865
Net cash provided by (used in) investing activities		81,649	(2,124,746)
Financing Activities
Borrowings under term loan			970,000
Repayments under term loan		(4,850)	(441,000)
Borrowings under senior notes			1,300,000
Payment of debt issuance costs			(55,893)
Repayments under equipment financing facilities and other		0	0
Proceeds from issuance of convertible preferred stock			400,000
Payment of stock issuance costs			(1,279)
Payment of dividends on preferred stock		(12,000)	(978)
Proceeds from issuance of common stock related to equity awards		1,559	5,317
Taxes paid related to net share settlement of equity awards		(3,617)	(3,933)
Intercompany activity		0	0
Net cash provided by (used in) financing activities		(18,908)	2,172,234
Effect of exchange rate changes on cash and cash equivalents		0	0
Net increase (decrease) in cash and cash equivalents		0	0
Cash and cash equivalents, beginning of period		0	0
Cash and cash equivalents, end of period		0	0
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Net cash provided by (used in) operating activities		(186,932)	77,948
Investing Activities
Purchases of property and equipment		(23,370)	(18,524)
Acquisition of businesses, net		(163,973)	0
Proceeds from the sale of assets		1,418	398
Intercompany activity		0	0
Net cash provided by (used in) investing activities		(185,925)	(18,126)
Financing Activities
Borrowings under term loan			0
Repayments under term loan		0	0
Borrowings under senior notes			0
Payment of debt issuance costs			(11,830)
Repayments under equipment financing facilities and other		(2,642)	(5,643)
Proceeds from issuance of convertible preferred stock			0
Payment of stock issuance costs			0
Payment of dividends on preferred stock		0	0
Proceeds from issuance of common stock related to equity awards		0	0
Taxes paid related to net share settlement of equity awards		0	0
Intercompany activity		(84,452)	(609,760)
Net cash provided by (used in) financing activities		236,670	(190,875)
Effect of exchange rate changes on cash and cash equivalents		0	0
Net increase (decrease) in cash and cash equivalents		(136,187)	(131,053)
Cash and cash equivalents, beginning of period		136,499	149,799
Cash and cash equivalents, end of period		312	18,746
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Net cash provided by (used in) operating activities		1,389	9,289
Investing Activities
Purchases of property and equipment		(169)	(1,259)
Acquisition of businesses, net		0	0
Proceeds from the sale of assets		10	15
Intercompany activity		0	0
Net cash provided by (used in) investing activities		(159)	(1,244)
Financing Activities
Borrowings under term loan			0
Repayments under term loan		0	0
Borrowings under senior notes			0
Payment of debt issuance costs			0
Repayments under equipment financing facilities and other		0	0
Proceeds from issuance of convertible preferred stock			0
Payment of stock issuance costs			0
Payment of dividends on preferred stock		0	0
Proceeds from issuance of common stock related to equity awards		0	0
Taxes paid related to net share settlement of equity awards		0	0
Intercompany activity		(2,323)	923
Net cash provided by (used in) financing activities		(3,018)	(2,231)
Effect of exchange rate changes on cash and cash equivalents		162	800
Net increase (decrease) in cash and cash equivalents		(1,626)	6,614
Cash and cash equivalents, beginning of period		1,959	1,582
Cash and cash equivalents, end of period		333	8,196
Eliminations and Other [Member]
Net cash provided by (used in) operating activities		6,140	217
Investing Activities
Purchases of property and equipment		0	0
Acquisition of businesses, net		0	0
Proceeds from the sale of assets		0	0
Intercompany activity		(84,430)	(606,865)
Net cash provided by (used in) investing activities		(84,430)	(606,865)
Financing Activities
Borrowings under term loan			0
Repayments under term loan		0	0
Borrowings under senior notes			0
Payment of debt issuance costs			0
Repayments under equipment financing facilities and other		0	0
Proceeds from issuance of convertible preferred stock			0
Payment of stock issuance costs			0
Payment of dividends on preferred stock		0	0
Proceeds from issuance of common stock related to equity awards		0	0
Taxes paid related to net share settlement of equity awards		0	0
Intercompany activity		86,775	608,837
Net cash provided by (used in) financing activities		86,775	608,837
Effect of exchange rate changes on cash and cash equivalents		46	0
Net increase (decrease) in cash and cash equivalents		8,531	2,189
Cash and cash equivalents, beginning of period		(8,531)	(13,131)
Cash and cash equivalents, end of period		0	(10,942)
Revolving Lines of Credit [Member]
Financing Activities
Borrowings under revolving lines of credit		1,880,684	1,530,667
Repayments under revolving lines of credit		(1,557,615)	(1,097,463)
Revolving Lines of Credit [Member] | Reportable Legal Entities [Member] | Parent Company [Member]
Financing Activities
Borrowings under revolving lines of credit		0	0
Repayments under revolving lines of credit		0	0
Revolving Lines of Credit [Member] | Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Financing Activities
Borrowings under revolving lines of credit		1,867,135	1,514,102
Repayments under revolving lines of credit		(1,543,371)	(1,077,744)
Revolving Lines of Credit [Member] | Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Financing Activities
Borrowings under revolving lines of credit		13,549	16,565
Repayments under revolving lines of credit		(14,244)	(19,719)
Revolving Lines of Credit [Member] | Eliminations and Other [Member]
Financing Activities
Borrowings under revolving lines of credit		0	0
Repayments under revolving lines of credit		$ 0	$ 0