SHARE-BASED COMPENSATION: Stock options outstanding and exercisable (Details)	6 Months Ended
	Sep. 30, 2016 $ / shares shares
Stock options outstanding and exercisable by exercise price range
Options outstanding (in shares) | shares	3,058,089
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)	$ 14.60
Options exercisable (in shares) | shares	2,353,864
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 14.49
Range of exercise price per share from $0.85 to $9.99
Stock options outstanding and exercisable by exercise price range
Exercise price per share, low end of range (in dollars per share)	0.85
Exercise price per share, high end of range (in dollars per share)	$ 9.99
Options outstanding (in shares) | shares	581,070
Options outstanding - Weighted-average remaining contractual life	6 years 7 months 6 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 1.86
Options exercisable (in shares) | shares	403,973
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 1.80
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) | shares	1,611,798
Options outstanding - Weighted-average remaining contractual life	5 years 3 months 18 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 15.22
Options exercisable (in shares) | shares	1,294,109
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 14.59
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) | shares	845,669
Options outstanding - Weighted-average remaining contractual life	4 years 7 months 6 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 21.77
Options exercisable (in shares) | shares	646,008
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 21.95
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) | shares	19,552
Options outstanding - Weighted-average remaining contractual life	7 years 1 month 6 days
Options outstanding - Weighted-average exercise price per share (in dollars per share)	$ 32.85
Options exercisable (in shares) | shares	9,774
Options exercisable - Weighted-average exercise price per share (in dollars per share)	$ 32.85