RESTRUCTURING CHARGES - Narrative (Details) $ in Thousands	3 Months Ended				6 Months Ended			12 Months Ended
	Sep. 30, 2018 USD ($)	Dec. 31, 2017 Employee	Sep. 30, 2017 USD ($)	Mar. 31, 2017 Employee	Mar. 31, 2019 USD ($) Employee	Sep. 30, 2018 USD ($) Employee	Sep. 30, 2017 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 2,472		$ 291			$ 3,619	$ 458
Q4 FY2017 Plan
Restructuring Cost and Reserve [Line Items]
Number of employees terminated | Employee				41
Q4 FY2017 Plan | Employee-Related
Restructuring Cost and Reserve [Line Items]
Restructuring charges							$ 700		$ 1,900
Q4 FY2017 Plan | Facility-Related
Restructuring Cost and Reserve [Line Items]
Restructuring charges									$ 400
Q3 FY 2018 Plan
Restructuring Cost and Reserve [Line Items]
Number of employees terminated | Employee		61
Restructuring charges						$ 1,700
Q3 FY 2018 Plan | Employee-Related
Restructuring Cost and Reserve [Line Items]
Restructuring charges								$ 5,100
VSP
Restructuring Cost and Reserve [Line Items]
Number of employees terminated | Employee						23
Restructuring charges						$ 2,300
Scenario, Forecast | VSP
Restructuring Cost and Reserve [Line Items]
Number of employees terminated | Employee					141
Restructuring charges					$ 16,100