SHARE-BASED COMPENSATION: Stock options outstanding and exercisable (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Stock options outstanding and exercisable by exercise price range
Options outstanding (in shares)	2,414,019
Options outstanding - Weighted-average remaining contractual life	5 years 1 month
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 13.86
Options exercisable (in shares)	2,169,170
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 14.58
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)	545,583
Options outstanding - Weighted-average remaining contractual life	5 years 2 months 18 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 1.62
Options exercisable (in shares)	390,000
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 1.71
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)	1,176,361
Options outstanding - Weighted-average remaining contractual life	4 years 4 months 14 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 14.95
Options exercisable (in shares)	1,092,595
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 14.74
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)	672,523
Options outstanding - Weighted-average remaining contractual life	6 years 2 months 16 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 21.30
Options exercisable (in shares)	667,023
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 21.30
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	5 years 4 months 13 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 32.85
Options exercisable (in shares)	19,552
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	$ 1.0	$ 1.4
Share-based compensation not yet recognized	$ 6.3
Period for recognition of unrecognized stock-based compensation expense	3 years