CONSOLIDATING GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidating Statements of Operations and Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019
Condensed Income Statements, Captions [Line Items]
Revenue	$ 632,061			$ 574,970			$ 1,746,849	$ 1,635,125
Cost of goods and services	467,058			420,487			1,279,893	1,200,092
Gross profit	165,003			154,483			466,956	435,033
Selling, general and administrative expenses	113,509			117,989			357,774	343,526
Income from operations	51,494			36,494			109,182	91,507
Other income (expense)
Interest income (expense), net	(16,585)			(17,087)			(49,096)	(50,723)
Loss from debt extinguishment, net	(1,235)			0			(7,925)	0
Other, net	806			979			2,199	3,251
Total other expense, net	(17,014)			(16,108)			(54,822)	(47,472)
Income before taxes from continuing operations	34,480			20,386			54,360	44,035
Provision (benefit) for income taxes	12,649			6,258			21,022	14,664
Income (loss) before equity in net income of subsidiaries	21,831			14,128			33,338	29,371
Equity in net income (loss) of subsidiaries	0			0			0	0
Income from continuing operations	21,831			14,128			33,338	29,371
Loss from operations of discontinued operations	0			0			0	(11,000)
Provision (benefit) for income taxes	0			533			0	(2,821)
Loss from discontinued operations	0			(533)			0	(8,179)
Net income	21,831	$ 895	$ 10,612	13,595	$ (1,156)	$ 8,753	33,338	21,192
Comprehensive income (loss)	30,533			12,560			34,047	17,587
Reportable Legal Entities | Parent Company
Condensed Income Statements, Captions [Line Items]
Revenue	0			0			0	0
Cost of goods and services	0			0			0	0
Gross profit	0			0			0	0
Selling, general and administrative expenses	5,229			5,342			19,169	15,651
Income from operations	(5,229)			(5,342)			(19,169)	(15,651)
Other income (expense)
Interest income (expense), net	(7,013)			(7,171)			(20,217)	(20,806)
Loss from debt extinguishment, net	(1,235)						(7,925)
Other, net	126			4,963			(389)	4,228
Total other expense, net	(8,122)			(2,208)			(28,531)	(16,578)
Income before taxes from continuing operations	(13,351)			(7,550)			(47,700)	(32,229)
Provision (benefit) for income taxes	(3,533)			(4,815)			(17,355)	(12,592)
Income (loss) before equity in net income of subsidiaries	(9,818)			(2,735)			(30,345)	(19,637)
Equity in net income (loss) of subsidiaries	31,649			16,330			63,683	40,829
Income from continuing operations				13,595				21,192
Loss from operations of discontinued operations				0				0
Provision (benefit) for income taxes				0				0
Loss from discontinued operations				0				0
Net income	21,831			13,595			33,338	21,192
Comprehensive income (loss)	30,533			12,560			34,047	17,587
Reportable Legal Entities | Guarantor Companies
Condensed Income Statements, Captions [Line Items]
Revenue	515,083			470,228			1,418,975	1,352,211
Cost of goods and services	385,717			350,197			1,058,556	1,013,676
Gross profit	129,366			120,031			360,419	338,535
Selling, general and administrative expenses	85,512			85,885			264,698	255,674
Income from operations	43,854			34,146			95,721	82,861
Other income (expense)
Interest income (expense), net	(9,537)			(9,048)			(28,916)	(27,306)
Loss from debt extinguishment, net	0						0
Other, net	(2,852)			(15,918)			(6,870)	(14,102)
Total other expense, net	(12,389)			(24,966)			(35,786)	(41,408)
Income before taxes from continuing operations	31,465			9,180			59,935	41,453
Provision (benefit) for income taxes	10,843			9,124			22,648	20,390
Income (loss) before equity in net income of subsidiaries	20,622			56			37,287	21,063
Equity in net income (loss) of subsidiaries	10,920			15,641			26,457	33,337
Income from continuing operations				15,697				54,400
Loss from operations of discontinued operations				0				0
Provision (benefit) for income taxes				0				0
Loss from discontinued operations				0				0
Net income	31,542			15,697			63,744	54,400
Comprehensive income (loss)	36,940			(597)			63,744	58,450
Reportable Legal Entities | Non-Guarantor Companies
Condensed Income Statements, Captions [Line Items]
Revenue	126,847			118,694			357,812	311,219
Cost of goods and services	91,541			84,568			252,331	215,786
Gross profit	35,306			34,126			105,481	95,433
Selling, general and administrative expenses	22,913			27,252			74,237	72,478
Income from operations	12,393			6,874			31,244	22,955
Other income (expense)
Interest income (expense), net	(35)			(868)			37	(2,611)
Loss from debt extinguishment, net	0						0
Other, net	4,004			12,762			10,844	14,479
Total other expense, net	3,969			11,894			10,881	11,868
Income before taxes from continuing operations	16,362			18,768			42,125	34,823
Provision (benefit) for income taxes	5,335			1,961			15,729	6,878
Income (loss) before equity in net income of subsidiaries	11,027			16,807			26,396	27,945
Equity in net income (loss) of subsidiaries	20,622			56			37,287	21,063
Income from continuing operations				16,863				49,008
Loss from operations of discontinued operations				0				(11,000)
Provision (benefit) for income taxes				533				(2,821)
Loss from discontinued operations				(533)				(8,179)
Net income	31,649			16,330			63,683	40,829
Comprehensive income (loss)	26,251			32,624			63,683	36,779
Elimination
Condensed Income Statements, Captions [Line Items]
Revenue	(9,869)			(13,952)			(29,938)	(28,305)
Cost of goods and services	(10,200)			(14,278)			(30,994)	(29,370)
Gross profit	331			326			1,056	1,065
Selling, general and administrative expenses	(145)			(490)			(330)	(277)
Income from operations	476			816			1,386	1,342
Other income (expense)
Interest income (expense), net	0			0			0	0
Loss from debt extinguishment, net	0						0
Other, net	(472)			(828)			(1,386)	(1,354)
Total other expense, net	(472)			(828)			(1,386)	(1,354)
Income before taxes from continuing operations	4			(12)			0	(12)
Provision (benefit) for income taxes	4			(12)			0	(12)
Income (loss) before equity in net income of subsidiaries	0			0			0	0
Equity in net income (loss) of subsidiaries	(63,191)			(32,027)			(127,427)	(95,229)
Income from continuing operations				(32,027)				(95,229)
Loss from operations of discontinued operations				0				0
Provision (benefit) for income taxes				0				0
Loss from discontinued operations				0				0
Net income	(63,191)			(32,027)			(127,427)	(95,229)
Comprehensive income (loss)	$ (63,191)			$ (32,027)			$ (127,427)	$ (95,229)