RESTRUCTURING, IMPAIRMENT AND OTHER CHARGES: Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments	$ 489	$ 2,834	$ 491	$ 2,831
Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments			500		$ 2,800	$ 6,500
Restructuring Activity2015 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments							$ 9,200
Employee Severance | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments					200
Employee Severance | Restructuring Activity 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments			800
Restructuring reserve	400		400
Employee Severance | Restructuring Activity2015 | 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					$ 2,600	3,000
Leased office facilities | 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 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments						1,500
Contract Termination | Restructuring Activity2015 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments							4,700
Leasehold Improvement Write Offs | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments						$ 2,100
Leasehold Improvement Write Offs | Restructuring Activity2015 | Gains Losses And Other Items Net
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments							2,000
United States Australia China And Europe | Employee Severance | Restructuring Activity2015
Restructuring Cost and Reserve [Line Items]
Restructuring charges and adjustments							$ 2,600
Restructuring reserve	$ 300		$ 300