SHARE-BASED COMPENSATION: Performance Stock Option Unit Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercised (in dollars per share)		$ 9.59
Number of shares
Outstanding at beginning of the period (in shares)		2,456,184
Forfeited or cancelled (in shares)		(18,646)
Outstanding at end of the period (in shares)	2,456,184	2,164,529		2,456,184
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
Forfeited or cancelled (in dollars per share)		19.07
Outstanding at the end of the period (in dollars per share)	$ 13.30	13.72		$ 13.30
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
Outstanding at the end of the period		$ 75,248
Exercisable at the end of the period		66,462
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		17,500	$ 14,900
Performance stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Future expense for performance stock option units		$ 800
Period for recognition of unrecognized stock-based compensation expense		3 years
Number of shares
Outstanding at beginning of the period (in shares)		322,823
Forfeited or cancelled (in shares)		(186,090)
Outstanding at end of the period (in shares)	322,823	136,733		322,823
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)		$ 21.42
Forfeited or cancelled (in dollars per share)		21.41
Outstanding at the end of the period (in dollars per share)	$ 21.42	21.44		$ 21.42
Exercisable at the end of the period (in dollars per share)		$ 0
Weighted-average remaining contractual term
Weighted average remaining contractual term		1 year 7 months 6 days
Exercisable at the end of the period		0 years
Aggregate intrinsic value
Outstanding at the end of the period		$ 3,698
Exercisable at the end of the period		$ 0
Performance stock | Shares Vesting Based On Relevant Performance Period At March 31 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units reached maturity	161,412
Vesting percentage				0.00%