SHARE-BASED COMPENSATION: Stock options outstanding and exercisable (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Stock options outstanding and exercisable by exercise price range
Options outstanding (in shares)	2,872,260
Options outstanding - Weighted-average remaining contractual life	6 years 20 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 13.40
Options exercisable (in shares)	2,174,071
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 13.65
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)	746,976
Options outstanding - Weighted-average remaining contractual life	6 years 9 months 5 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 1.68
Options exercisable (in shares)	473,841
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 1.74
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)	1,305,746
Options outstanding - Weighted-average remaining contractual life	5 years 29 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 14.99
Options exercisable (in shares)	1,109,428
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 14.50
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)	799,986
Options outstanding - Weighted-average remaining contractual life	6 years 11 months 22 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 21.29
Options exercisable (in shares)	576,139
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)	19,552
Options outstanding - Weighted-average remaining contractual life	6 years 1 month 12 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 32.85
Options exercisable (in shares)	14,663
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	$ 2.8	$ 3.5
Share-based compensation not yet recognized	$ 8.5
Period for recognition of unrecognized stock-based compensation expense	4 years