SHARE-BASED COMPENSATION: Stock options outstanding and exercisable (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Stock options outstanding and exercisable by exercise price range
Options outstanding (in shares)	2,164,529
Options outstanding - Weighted-average remaining contractual life	4 years 10 months 24 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 13.72
Options exercisable (in shares)	1,951,500
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 14.43
Range of exercise price per share from $0.61 to $9.99
Stock options outstanding and exercisable by exercise price range
Exercise price per share, low end of range (in dollars per share)	0.61
Exercise price per share, high end of range (in dollars per share)	$ 9.99
Options outstanding (in shares)	478,039
Options outstanding - Weighted-average remaining contractual life	5 years 4 months 24 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 1.37
Options exercisable (in shares)	341,363
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 1.35
Range of exercise price per share from $10.00 to $19.99
Stock options outstanding and exercisable by exercise price range
Exercise price per share, low end of range (in dollars per share)	10.00
Exercise price per share, high end of range (in dollars per share)	$ 19.99
Options outstanding (in shares)	1,043,507
Options outstanding - Weighted-average remaining contractual life	4 years 1 month 6 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 14.62
Options exercisable (in shares)	967,154
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 14.39
Range of exercise price per share from $20.00 to $24.99
Stock options outstanding and exercisable by exercise price range
Exercise price per share, low end of range (in dollars per share)	20.00
Exercise price per share, high end of range (in dollars per share)	$ 24.99
Options outstanding (in shares)	636,293
Options outstanding - Weighted-average remaining contractual life	5 years 10 months 24 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 21.31
Options exercisable (in shares)	636,293
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 21.31
Range of exercise price per share from $25.00 to $32.85
Stock options outstanding and exercisable by exercise price range
Exercise price per share, low end of range (in dollars per share)	25.00
Exercise price per share, high end of range (in dollars per share)	$ 32.85
Options outstanding (in shares)	6,690
Options outstanding - Weighted-average remaining contractual life	5 years 1 month 6 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 32.85
Options exercisable (in shares)	6,690
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 32.85
Stock options
Stock options outstanding and exercisable by exercise price range
Share-based compensation expense	$ 1.7	$ 2.7
Share-based compensation not yet recognized	$ 4.3
Period for recognition of unrecognized stock-based compensation expense	3 years