ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,029,999	$ 980,377	$ 1,008,167	$ 980,377	$ 666,692
Other comprehensive income, net of tax	(37,032)		(7,215)	(16,922)	(5,041)
Other comprehensive income, net of tax, including stranded tax effect				(17,410)
Balance at end of period	1,009,410	1,029,999	1,025,867	1,009,410	1,025,867
Effect of the adoption of the stranded tax effect accounting standards		0
Accounting Standards Update 2018-02 [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income, before tax	0		0	(497)	0
Reclassification from AOCI, tax	0		0	9	0
Reclassification from AOCI, net of tax	0		0	(488)	0
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(3,616)	(23,238)	6,713	(23,238)	4,539
Balance at end of period	(40,648)	(3,616)	(502)	(40,648)	(502)
Effect of the adoption of the stranded tax effect accounting standards		$ (488)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income, before tax	(19,752)		(1,621)	(3,935)	1,412
Reclassification from AOCI, tax	27		629	61	21
Reclassification from AOCI, net of tax	(19,725)		(992)	(3,874)	1,433
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, net of tax	0		251	0	0
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income, before tax	1,366		(1)	2,537	(1)
Reclassification from AOCI, tax	4,982		1,879	3,755	1,879
Reclassification from AOCI, net of tax	(17,307)		(6,474)	(13,048)	(6,474)
Change in fair value	$ (23,655)		$ (8,352)	$ (19,340)	$ (8,352)

Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent, Including Stranded Tax Effect

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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Amount before tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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Amount of increase (decrease) in accumulated other comprehensive income (AOCI) for reclassification to retained earnings of tax effect from remeasurement of deferred tax pursuant to Tax Cuts and Jobs Act.

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