RESTRUCTURING, IMPAIRMENT AND OTHER CHARGES: Narrative (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments	$ (5)		$ 233	$ 1,197	$ 1,890
Restructuring reserve	4,200			4,200
Business exit costs		$ 1,000
Adjustment to existing restructured leases		$ (900)
Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments				1,200
Restructuring Activity 2020 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments						$ 3,400
Restructuring Activity 2019 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments							$ 7,700
Restructuring Activity 2018 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments								$ 2,700
Restructuring Activity 2017 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments									$ 3,000
Restructuring Activity 2015 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments										$ 9,300
Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	100			100
Employee Severance | Restructuring Activity 2018 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments								200
Employee Severance | Restructuring Activity 2015 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments										2,600
Termination Of Associates | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments				100
Termination Of Associates | Restructuring Activity 2020 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments						1,100
Termination Of Associates | Restructuring Activity 2019 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments							800
Termination Of Associates | Restructuring Activity 2018 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments								$ 2,500
Termination Of Associates | Restructuring Activity 2017 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments									3,000
Leased office facilities | Restructuring Activity 2017 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments									1,500
Adjustments to estimates related to the fiscal 2015 lease accruals | Restructuring Activity 2017 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments									$ 1,500
Contract Termination | Restructuring Activity 2015 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments										4,700
Leasehold Improvement Write Offs | Restructuring Activity 2019 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments							800
Leasehold Improvement Write Offs | Restructuring Activity 2015 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments										$ 2,000
United States and Europe | Employee Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments				1,100
United States | Employee Severance | Restructuring Activity 2020
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments						1,700
Asia-Pacific ("APAC") | Employee Severance | Restructuring Activity 2020
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments						$ 600
United States Australia China And Europe | Employee Severance | Restructuring Activity 2019
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments							$ 6,100
United States Australia China And Europe | Employee Severance | Restructuring Activity 2015
Restructuring Cost and Reserve [Line Items]
Restructuring reserve	$ 200			$ 200