Supplemental Guarantor Information - Condensed Consolidating Statements of Operations (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net sales		$ 1,924,534	$ 1,934,951	$ 5,075,247	$ 4,482,555
Cost of products sold		1,451,998	1,441,057	3,832,154	3,380,531
Gross profit		472,536	493,894	1,243,093	1,102,024
Operating expense:
Selling, general and administrative		328,827	323,194	976,928	858,534
Depreciation		17,731	15,811	52,779	41,640
Amortization		51,724	50,076	155,508	105,339
Total operating expense		398,282	389,081	1,185,215	1,005,513
Intercompany charges (income)		0	0	0	0
Income (loss) from operations		74,254	104,813	57,878	96,511
Interest expense, financing costs, and other		38,089	37,348	116,902	99,486
Intercompany interest expense (income)		0	0	0	0
Income (loss) before provision for income taxes		36,165	67,465	(59,024)	(2,975)
Provision for (benefit from) income taxes	[1]	5,178	18,090	(21,032)	(53,291)
Income (loss) before equity in net income of subsidiaries		30,987	49,375	(37,992)	50,316
Equity in net income of subsidiaries		0	0	0	0
Net income (loss)		30,987	49,375	(37,992)	50,316
Reportable Legal Entities [Member] | Parent Company [Member]
Net sales		0	0	0	0
Cost of products sold		0	0	0	0
Gross profit		0	0	0	0
Operating expense:
Selling, general and administrative		1,377	1,776	15,572	4,315
Depreciation		1,243	411	2,743	1,310
Amortization		0	0	0	0
Total operating expense		2,620	2,187	18,315	5,625
Intercompany charges (income)		(3,566)	(7,521)	(17,110)	(8,105)
Income (loss) from operations		946	5,334	(1,205)	2,480
Interest expense, financing costs, and other		41,332	33,416	103,574	90,712
Intercompany interest expense (income)		(17,558)	(6,809)	(28,447)	(17,698)
Income (loss) before provision for income taxes		(22,828)	(21,273)	(76,332)	(70,534)
Provision for (benefit from) income taxes		(13,241)	(6,848)	(28,280)	(11,796)
Income (loss) before equity in net income of subsidiaries		(9,587)	(14,425)	(48,052)	(58,738)
Equity in net income of subsidiaries		40,574	63,800	10,060	109,054
Net income (loss)		30,987	49,375	(37,992)	50,316
Reportable Legal Entities [Member] | Guarantor Subsidiaries [Member]
Net sales		1,870,923	1,883,249	4,956,220	4,364,128
Cost of products sold		1,409,632	1,401,045	3,737,845	3,288,086
Gross profit		461,291	482,204	1,218,375	1,076,042
Operating expense:
Selling, general and administrative		319,666	313,034	938,044	828,987
Depreciation		16,034	14,967	48,648	39,015
Amortization		51,616	49,947	155,180	104,946
Total operating expense		387,316	377,948	1,141,872	972,948
Intercompany charges (income)		3,566	7,521	17,110	8,105
Income (loss) from operations		70,409	96,735	59,393	94,989
Interest expense, financing costs, and other		(2,457)	3,594	13,503	8,226
Intercompany interest expense (income)		17,181	6,427	27,306	16,552
Income (loss) before provision for income taxes		55,685	86,714	18,584	70,211
Provision for (benefit from) income taxes		17,490	24,356	7,614	(40,891)
Income (loss) before equity in net income of subsidiaries		38,195	62,358	10,970	111,102
Equity in net income of subsidiaries		0	0	0	0
Net income (loss)		38,195	62,358	10,970	111,102
Reportable Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Net sales		53,611	51,702	119,027	118,427
Cost of products sold		42,366	40,012	94,309	92,445
Gross profit		11,245	11,690	24,718	25,982
Operating expense:
Selling, general and administrative		7,784	8,384	23,312	25,232
Depreciation		454	433	1,388	1,315
Amortization		108	129	328	393
Total operating expense		8,346	8,946	25,028	26,940
Intercompany charges (income)		0	0	0	0
Income (loss) from operations		2,899	2,744	(310)	(958)
Interest expense, financing costs, and other		(786)	338	(175)	548
Intercompany interest expense (income)		377	382	1,141	1,146
Income (loss) before provision for income taxes		3,308	2,024	(1,276)	(2,652)
Provision for (benefit from) income taxes		929	582	(366)	(604)
Income (loss) before equity in net income of subsidiaries		2,379	1,442	(910)	(2,048)
Equity in net income of subsidiaries		0	0	0	0
Net income (loss)		2,379	1,442	(910)	(2,048)
Eliminations and Other [Member]
Net sales		0	0	0	0
Cost of products sold		0	0	0	0
Gross profit		0	0	0	0
Operating expense:
Selling, general and administrative		0	0	0	0
Depreciation		0	0	0	0
Amortization		0	0	0	0
Total operating expense		0	0	0	0
Intercompany charges (income)		0	0	0	0
Income (loss) from operations		0	0	0	0
Interest expense, financing costs, and other		0	0	0	0
Intercompany interest expense (income)		0	0	0	0
Income (loss) before provision for income taxes		0	0	0	0
Provision for (benefit from) income taxes		0	0	0	0
Income (loss) before equity in net income of subsidiaries		0	0	0	0
Equity in net income of subsidiaries		(40,574)	(63,800)	(10,060)	(109,054)
Net income (loss)		$ (40,574)	$ (63,800)	$ (10,060)	$ (109,054)

[1] Three and nine months ended June 30, 2018 amounts include a net tax benefit of $1.2 million and $49.2 million, respectively, resulting from recording the provisional impact of the enactment of the 2017 Tax Cuts and Jobs Act (“TCJA”).