SHARE-BASED COMPENSATION: (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Sep. 30, 2018	Jun. 30, 2018
Stock Option Activity - Number of Shares
Outstanding at beginning of the period (in shares)	2,456,184
Exercised (in shares)	(273,009)
Forfeited or cancelled (in shares)	(18,646)
Outstanding at end of the period (in shares)	2,164,529
Exercisable at the end of the period (in shares)	1,951,500
Weighted-average exercise price per share
Outstanding at the beginning of the period (in dollars per share)	$ 13.30
Exercised (in dollars per share)	9.59
Forfeited or cancelled (in dollars per share)	19.07
Outstanding at the end of the period (in dollars per share)	13.72
Exercisable at the end of the period (in dollars per share)	$ 14.43
Weighted-average remaining contractual term
Weighted average remaining contractual term	4 years 10 months 24 days
Exercisable at the end of the period	4 years 8 months 12 days
Aggregate intrinsic value
Exercised	$ 7,144
Outstanding at the end of the period	75,248
Exercisable at the end of the period	$ 66,462
Stock Option and Equity Compensation Plans
Share-based compensation
Total shares reserved for issuance since inception of the stock option and equity compensation plans (in shares)	42,300,000	37,300,000
Shares which remained available for future grants (in shares)	13,000,000.0
Amended and Restated 2005 Equity Compensation Plan
Share-based compensation
Shares which remained available for future grants (in shares)	37,900,000	32,900,000