CONSOLIDATING GUARANTOR AND NON-GUARANTOR FINANCIAL INFORMATION - Condensed Consolidating Statements of Operations and Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2020	Mar. 31, 2019
Condensed Income Statements, Captions [Line Items]
Revenue	$ 566,350		$ 549,633		$ 1,114,788	$ 1,060,155
Cost of goods and services	414,318		412,129		812,835	779,605
Gross profit	152,032		137,504		301,953	280,550
Selling, general and administrative expenses	126,467		111,783		244,265	225,537
Income from operations	25,565		25,721		57,688	55,013
Other income (expense)
Interest income (expense), net	(16,561)		(17,305)		(32,511)	(33,636)
Loss from debt extinguishment, net	(6,690)		0		(6,690)	0
Other, net	615		1,268		1,393	2,272
Total other expense, net	(22,636)		(16,037)		(37,808)	(31,364)
Income before taxes from continuing operations	2,929		9,684		19,880	23,649
Provision (benefit) for income taxes	2,034		3,194		8,373	8,406
Income (loss) before equity in net income of subsidiaries	895		6,490		11,507	15,243
Equity in net income (loss) of subsidiaries	0		0		0	0
Income from continuing operations	895		6,490		11,507	15,243
Loss from operations of discontinued operations	0		(11,000)		0	(11,000)
Benefit for income taxes	0		(3,354)		0	(3,354)
Loss from discontinued operations	0		(7,646)		0	(7,646)
Net income (loss)	895	$ 10,612	(1,156)	$ 8,753	11,507	7,597
Comprehensive income (loss)	(13,939)		1,724		3,514	5,027
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	7,922		5,249		13,940	10,309
Income from operations	(7,922)		(5,249)		(13,940)	(10,309)
Other income (expense)
Interest income (expense), net	(6,880)		(7,328)		(13,204)	(13,635)
Loss from debt extinguishment, net	(6,690)				(6,690)
Other, net	(418)		(473)		(515)	(735)
Total other expense, net	(13,988)		(7,801)		(20,409)	(14,370)
Income before taxes from continuing operations	(21,910)		(13,050)		(34,349)	(24,679)
Provision (benefit) for income taxes	(9,427)		(4,242)		(13,822)	(7,777)
Income (loss) before equity in net income of subsidiaries	(12,483)		(8,808)		(20,527)	(16,902)
Equity in net income (loss) of subsidiaries	13,378		7,652		32,034	24,499
Income from continuing operations			(1,156)			7,597
Loss from operations of discontinued operations			0			0
Benefit for income taxes			0			0
Loss from discontinued operations			0			0
Net income (loss)	895		(1,156)		11,507	7,597
Comprehensive income (loss)	(13,939)		1,724		3,514	5,027
Reportable Legal Entities | Guarantor Companies
Condensed Income Statements, Captions [Line Items]
Revenue	462,500		462,739		903,892	881,983
Cost of goods and services	345,626		354,382		672,839	663,479
Gross profit	116,874		108,357		231,053	218,504
Selling, general and administrative expenses	91,338		84,813		179,186	169,789
Income from operations	25,536		23,544		51,867	48,715
Other income (expense)
Interest income (expense), net	(9,706)		(9,128)		(19,379)	(18,258)
Loss from debt extinguishment, net	0				0
Other, net	(2,667)		1,129		(4,018)	1,816
Total other expense, net	(12,373)		(7,999)		(23,397)	(16,442)
Income before taxes from continuing operations	13,163		15,545		28,470	32,273
Provision (benefit) for income taxes	6,078		5,292		11,805	11,266
Income (loss) before equity in net income of subsidiaries	7,085		10,253		16,665	21,007
Equity in net income (loss) of subsidiaries	6,341		11,646		15,537	17,696
Income from continuing operations			21,899			38,703
Loss from operations of discontinued operations			0			0
Benefit for income taxes			0			0
Loss from discontinued operations			0			0
Net income (loss)	13,426		21,899		32,202	38,703
Comprehensive income (loss)	8,028		5,448		26,804	59,017
Reportable Legal Entities | Non-Guarantor Companies
Condensed Income Statements, Captions [Line Items]
Revenue	113,926		94,285		230,965	192,525
Cost of goods and services	79,112		65,516		160,790	131,218
Gross profit	34,814		28,769		70,175	61,307
Selling, general and administrative expenses	27,300		21,409		51,324	45,226
Income from operations	7,514		7,360		18,851	16,081
Other income (expense)
Interest income (expense), net	25		(849)		72	(1,743)
Loss from debt extinguishment, net	0				0
Other, net	4,141		676		6,840	1,717
Total other expense, net	4,166		(173)		6,912	(26)
Income before taxes from continuing operations	11,680		7,187		25,763	16,055
Provision (benefit) for income taxes	5,387		2,142		10,394	4,917
Income (loss) before equity in net income of subsidiaries	6,293		5,045		15,369	11,138
Equity in net income (loss) of subsidiaries	7,085		10,253		16,665	21,007
Income from continuing operations			15,298			32,145
Loss from operations of discontinued operations			(11,000)			(11,000)
Benefit for income taxes			(3,354)			(3,354)
Loss from discontinued operations			(7,646)			(7,646)
Net income (loss)	13,378		7,652		32,034	24,499
Comprehensive income (loss)	18,776		8,736		37,432	4,185
Elimination
Condensed Income Statements, Captions [Line Items]
Revenue	(10,076)		(7,391)		(20,069)	(14,353)
Cost of goods and services	(10,420)		(7,769)		(20,794)	(15,092)
Gross profit	344		378		725	739
Selling, general and administrative expenses	(93)		312		(185)	213
Income from operations	437		66		910	526
Other income (expense)
Interest income (expense), net	0		0		0	0
Loss from debt extinguishment, net	0				0
Other, net	(441)		(64)		(914)	(526)
Total other expense, net	(441)		(64)		(914)	(526)
Income before taxes from continuing operations	(4)		2		(4)	0
Provision (benefit) for income taxes	(4)		2		(4)	0
Income (loss) before equity in net income of subsidiaries	0		0		0	0
Equity in net income (loss) of subsidiaries	(26,804)		(29,551)		(64,236)	(63,202)
Income from continuing operations			(29,551)			(63,202)
Loss from operations of discontinued operations			0			0
Benefit for income taxes			0			0
Loss from discontinued operations			0			0
Net income (loss)	(26,804)		(29,551)		(64,236)	(63,202)
Comprehensive income (loss)	$ (26,804)		$ (14,184)		$ (64,236)	$ (63,202)