STOCK-BASED COMPENSATION: Performance Stock Option Unit Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised (in dollars per share)	$ 5.68
Future expense for performance stock option units	$ 183,100
Number of shares
Outstanding at beginning of the period (in shares)	1,374,430
Forfeited or cancelled (in shares)	(2,340)
Outstanding at end of the period (in shares)	1,347,709
Exercisable at the end of the period (in shares)	1,278,265
Weighted-average exercise price per share
Outstanding at the beginning of the period (in dollars per share)	$ 14.81
Forfeited or cancelled (in dollars per share)	2.04
Outstanding at the end of the period (in dollars per share)	15.00
Exercisable at the end of the period (in dollars per share)	$ 15.73
Weighted-average remaining contractual term
Weighted average remaining contractual term	4 years 2 months 12 days
Exercisable at the end of the period	4 years
Aggregate intrinsic value
Outstanding at the end of the period	$ 45,125
Exercisable at the end of the period	41,859
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	11,100	$ 8,500
Performance stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 0	$ 300
Number of shares
Outstanding at beginning of the period (in shares)	130,154
Forfeited or cancelled (in shares)	(130,154)
Outstanding at end of the period (in shares)	0
Exercisable at the end of the period (in shares)	0
Weighted-average exercise price per share
Outstanding at the beginning of the period (in dollars per share)	$ 21.44
Forfeited or cancelled (in dollars per share)	21.44
Outstanding at the end of the period (in dollars per share)	0
Exercisable at the end of the period (in dollars per share)	$ 0
Weighted-average remaining contractual term
Weighted average remaining contractual term
Aggregate intrinsic value
Outstanding at the end of the period	$ 0
Exercisable at the end of the period	$ 0