ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 1,009,410	$ 1,025,867	$ 980,377	$ 666,692
Other comprehensive income, net of tax	8,752	(6,345)	(8,170)	(11,386)
Other comprehensive income, net of tax, including stranded tax effect			(8,658)
Balance at end of period	1,025,034	1,025,333	1,025,034	1,025,333
Effect of adoption of the stranded tax effect account standard
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	(40,648)	(502)	(23,238)	4,539
Balance at end of period	(31,896)	(6,847)	(31,896)	(6,847)
Accumulated foreign currency adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income, before tax	9,048	3,284	5,113	4,696
Reclassification from AOCI, tax	38	(585)	99	(564)
Reclassification from AOCI, net of tax	9,086	2,699	5,212	4,132
Change in pension and other postretirement
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income, before tax	3,262	(39)	5,799	(40)
Reclassification from AOCI, tax	98	2,630	3,853	4,509
Reclassification from AOCI, net of tax	(334)	(9,044)	(13,382)	(15,518)
Change in fair value	$ (3,694)	$ (11,635)	$ (23,034)	$ (19,987)