CONSOLIDATING GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION (Details) - Summary of consolidated statement of operations and comprehensive income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Condensed Income Statements, Captions [Line Items]
Revenue	$ 660,673	$ 632,061	$ 566,350	$ 548,438	$ 574,164	$ 574,970	$ 549,633	$ 510,522	$ 2,407,522	$ 2,209,289	$ 1,977,918
Cost of goods and services									1,766,096	1,625,815	1,466,600
Gross profit	174,470	165,003	152,032	149,921	158,458	151,699	133,537	139,780	641,426	583,474	511,318
Selling, general and administrative expenses									486,398	447,163	418,517
Income from continuing operations									155,028	136,311	92,801
Other income (expense)
Interest income (expense), net									(65,791)	(67,260)	(63,871)
Loss from debt extinguishment		969	5,245						7,925	0	0
Other, net									1,445	3,127	4,880
Total other income (expense)									(72,271)	(64,133)	(58,991)
Income before taxes from continuing operations									82,757	72,178	33,810
Provision for income taxes									29,328	26,556	555
Income (loss) before equity in net income of subsidiaries									53,429	45,622	33,255
Equity in net income (loss) of subsidiaries									0	0	0
Income (loss) from continuing operations	$ 20,091	$ 21,831	$ 895	$ 10,612	$ 16,251	$ 14,128	$ 6,490	$ 8,753	53,429	45,622	33,255
Income (loss) from operations of discontinued businesses									0	(11,050)	119,981
Provision for income taxes									0	(2,715)	27,558
Income (loss) from discontinued operations									0	(8,335)	92,423
Net income									53,429	37,287	125,678
Comprehensive income (loss)									47,253	5,483	152,047
Parent Company
Condensed Income Statements, Captions [Line Items]
Revenue									0	0	0
Cost of goods and services									0	0	0
Gross profit									0	0	0
Selling, general and administrative expenses									24,876	22,566	37,540
Income from continuing operations									(24,876)	(22,566)	(37,540)
Other income (expense)
Interest income (expense), net									(27,129)	(27,883)	(23,911)
Loss from debt extinguishment									7,925
Other, net									(523)	(778)	(7,666)
Total other income (expense)									(35,577)	(28,661)	(31,577)
Income before taxes from continuing operations									(60,453)	(51,227)	(69,117)
Provision for income taxes									(11,907)	(7,425)	(17,692)
Income (loss) before equity in net income of subsidiaries									(48,546)	(43,802)	(51,425)
Equity in net income (loss) of subsidiaries									101,975	81,089	177,103
Income (loss) from continuing operations										37,287	125,678
Income (loss) from operations of discontinued businesses										0	0
Provision for income taxes										0	0
Income (loss) from discontinued operations										0	0
Net income									53,429	37,287	125,678
Comprehensive income (loss)									47,253	5,483	152,047
Guarantor Companies
Condensed Income Statements, Captions [Line Items]
Revenue									1,938,972	1,808,824	1,638,792
Cost of goods and services									1,450,924	1,353,663	1,250,261
Gross profit									488,048	455,161	388,531
Selling, general and administrative expenses									357,901	327,306	290,475
Income from continuing operations									130,147	127,855	98,056
Other income (expense)
Interest income (expense), net									(38,301)	(39,288)	(31,913)
Loss from debt extinguishment									0
Other, net									(7,946)	(17,699)	125,531
Total other income (expense)									(46,247)	(56,987)	93,618
Income before taxes from continuing operations									83,900	70,868	191,674
Provision for income taxes									25,445	20,534	9,546
Income (loss) before equity in net income of subsidiaries									58,455	50,334	182,128
Equity in net income (loss) of subsidiaries									43,505	44,303	(151,864)
Income (loss) from continuing operations										94,637	30,264
Income (loss) from operations of discontinued businesses										0	119,981
Provision for income taxes										0	27,558
Income (loss) from discontinued operations										0	92,423
Net income									101,960	94,637	122,687
Comprehensive income (loss)									101,960	87,851	143,936
Non-Guarantor Companies
Condensed Income Statements, Captions [Line Items]
Revenue									507,621	437,542	367,149
Cost of goods and services									355,696	310,707	245,687
Gross profit									151,925	126,835	121,462
Selling, general and administrative expenses									103,991	97,661	90,872
Income from continuing operations									47,934	29,174	30,590
Other income (expense)
Interest income (expense), net									(361)	(89)	(8,047)
Loss from debt extinguishment									0
Other, net									11,762	23,452	(111,248)
Total other income (expense)									11,401	23,363	(119,295)
Income before taxes from continuing operations									59,335	52,537	(88,705)
Provision for income taxes									15,788	13,447	8,743
Income (loss) before equity in net income of subsidiaries									43,547	39,090	(97,448)
Equity in net income (loss) of subsidiaries									58,455	50,334	182,128
Income (loss) from continuing operations										89,424	84,680
Income (loss) from operations of discontinued businesses										(11,050)	0
Provision for income taxes										(2,715)	0
Income (loss) from discontinued operations										(8,335)	0
Net income									102,002	81,089	84,680
Comprehensive income (loss)									102,002	87,875	81,389
Elimination
Condensed Income Statements, Captions [Line Items]
Revenue									(39,071)	(37,077)	(28,023)
Cost of goods and services									(40,524)	(38,555)	(29,348)
Gross profit									1,453	1,478	1,325
Selling, general and administrative expenses									(370)	(370)	(370)
Income from continuing operations									1,823	1,848	1,695
Other income (expense)
Interest income (expense), net									0	0	0
Loss from debt extinguishment									0
Other, net									(1,848)	(1,848)	(1,737)
Total other income (expense)									(1,848)	(1,848)	(1,737)
Income before taxes from continuing operations									(25)	0	(42)
Provision for income taxes									2	0	(42)
Income (loss) before equity in net income of subsidiaries									(27)	0	0
Equity in net income (loss) of subsidiaries									(203,935)	(175,726)	(207,367)
Income (loss) from continuing operations										(175,726)	(207,367)
Income (loss) from operations of discontinued businesses										0	0
Provision for income taxes										0	0
Income (loss) from discontinued operations										0	0
Net income									(203,962)	(175,726)	(207,367)
Comprehensive income (loss)									$ (203,962)	$ (175,726)	$ (225,325)