ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Components of Accumulated Comprehensive Income [Roll Forward]
Balance at beginning of period	$ 666,692	$ 595,037
Foreign currency translation adjustment, net of tax	2,425	7,144
Available-for-sale securities adjustments, net of tax	0	(46)
Change in fair value, net of tax		229
Reclassification adjustment into earnings, net of tax		(30)
Minimum pension liability adjustment	(251)	0
Balance at end of period	1,008,167	601,667
Other Comprehensive Income, Tax [Abstract]
Foreign currency translation adjustment, tax	608	(1,150)
Available-for-sale securities adjustments, tax		0
Change in fair value, tax		80
Reclassification adjustment into earnings, tax		(11)
Change in pension and other postretirement liabilities, tax	0
Accumulated Other Comprehensive Income [Member]
Components of Accumulated Comprehensive Income [Roll Forward]
Balance at beginning of period	4,539	3,949
Foreign currency translation adjustment, net of tax	2,425	7,144
Available-for-sale securities adjustments, net of tax		(46)
Minimum pension liability adjustment	(251)
Balance at end of period	6,713	11,246
Foreign Currency Translation [Member]
Components of Accumulated Comprehensive Income [Roll Forward]
Balance at beginning of period	5,918	5,239
Foreign currency translation adjustment, net of tax	2,425	7,144
Balance at end of period	8,343	12,383
Cash Flow Hedges [Member]
Components of Accumulated Comprehensive Income [Roll Forward]
Balance at beginning of period	(17)	46
Change in fair value, net of tax		229
Reclassification adjustment into earnings, net of tax		(30)
Balance at end of period	(17)	245
Pension and Other Postretirement Liabilities [Member]
Components of Accumulated Comprehensive Income [Roll Forward]
Balance at beginning of period	(1,362)	(1,336)
Minimum pension liability adjustment	(251)
Balance at end of period	$ (1,613)	(1,336)
Available-For-Sale Securities
Components of Accumulated Comprehensive Income [Roll Forward]
Available-for-sale securities adjustments, net of tax		(46)
Balance at end of period		$ (46)