PENSION PLANS AND OTHER POST RETIREMENT BENEFITS - Schedule of the Change in Benefit Obligation (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation—beginning of fiscal year	$ 67,226	$ 69,479	$ 69,479
Service cost	598	520	2,138
Interest cost	306	283	1,164
Benefits paid	(430)		(2,362)
Actuarial (gain) loss	2,572		(2,823)
Foreign exchange (gain) loss	2,138		(370)
Benefit obligation—end of period	72,410		67,226
Less: Current portion	(1,949)		(1,835)
Non-current portion of benefit obligation	70,461		65,391
CDT
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation—beginning of fiscal year	32,851	35,836	35,836
Service cost	116	142	572
Interest cost	124	114	459
Benefits paid	(180)		(644)
Actuarial (gain) loss	1,859		(3,073)
Foreign exchange (gain) loss	1,028		(299)
Benefit obligation—end of period	35,798		32,851
Less: Current portion	(818)		(777)
Non-current portion of benefit obligation	34,980		32,074
GXS GER
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation—beginning of fiscal year	24,105	26,739	26,739
Service cost	51	79	319
Interest cost	89	84	337
Benefits paid	(250)		(926)
Actuarial (gain) loss	1,486		(2,083)
Foreign exchange (gain) loss	755		(281)
Benefit obligation—end of period	26,236		24,105
Less: Current portion	(980)		(943)
Non-current portion of benefit obligation	25,256		23,162
GXS PHP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation—beginning of fiscal year	10,270	6,904	6,904
Service cost	431	299	1,247
Interest cost	93	$ 85	368
Benefits paid	0		(792)
Actuarial (gain) loss	(773)		2,333
Foreign exchange (gain) loss	355		210
Benefit obligation—end of period	10,376		10,270
Less: Current portion	(151)		(115)
Non-current portion of benefit obligation	$ 10,225		$ 10,155