SHARE-BASED COMPENSATION: Performance Stock Option Unit Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised (in dollars per share)		$ 16.31
Number of shares
Outstanding at beginning of the period (in shares)		3,033,071
Forfeited or cancelled (in shares)		(63,540)
Outstanding at end of the period (in shares)	2,872,260	2,872,260		3,033,071
Exercisable at the end of the period (in shares)	2,174,071	2,174,071
Weighted-average exercise price per share
Outstanding at the beginning of the period (in dollars per share)		$ 13.14
Forfeited or cancelled (in dollars per share)		20.20
Outstanding at the end of the period (in dollars per share)	$ 13.40	13.40		$ 13.14
Exercisable at the end of the period (in dollars per share)	$ 13.65	$ 13.65
Weighted-average remaining contractual term
Weighted average remaining contractual term		6 years 20 days
Exercisable at the end of the period		5 years 4 months 23 days
Aggregate intrinsic value
Outstanding at the end of the period	$ 32,439	$ 32,439
Exercisable at the end of the period	24,016	$ 24,016
Shares Vesting Based On Relevent Performance Period At March 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units reached maturity		183,322
Vesting percentage		163.00%
Options issued (in shares)		299,641
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		$ 18,600	$ 15,400
Restricted stock units | Shares Vesting Based On Relevent Performance Period At March 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units reached maturity				157,985
Vesting percentage		160.00%
Options issued (in shares)		252,760
Restricted stock units | Performance stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options issued (in shares)		94,775
Performance stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised (in dollars per share)		$ 21.32
Share-based compensation expense		$ 800	$ 300
Future expense for performance stock option units	$ 2,800	$ 2,800
Period for recognition of unrecognized stock-based compensation expense		4 years
Number of shares
Outstanding at beginning of the period (in shares)		555,123
Performance units converted to options (in shares)		(183,322)
Forfeited or cancelled (in shares)		(11,291)
Outstanding at end of the period (in shares)	360,510	360,510		555,123
Exercisable at the end of the period (in shares)	0	0
Weighted-average exercise price per share
Outstanding at the beginning of the period (in dollars per share)		$ 21.41
Performance units converted to options (in dollars per share)		21.41
Forfeited or cancelled (in dollars per share)		21.32
Outstanding at the end of the period (in dollars per share)	$ 21.41	21.41		$ 21.41
Exercisable at the end of the period (in dollars per share)	$ 0.00	$ 0.00
Weighted-average remaining contractual term
Weighted average remaining contractual term		2 years 1 month 22 days
Exercisable at the end of the period	0 years
Aggregate intrinsic value
Outstanding at the end of the period	$ 1,168	$ 1,168
Exercisable at the end of the period	$ 0	$ 0