INCOME TAXES (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating Loss Carryforwards [Line Items]
Forecasted effective tax rate	13.10%	10.30%
Forecasted tax credits, net of deferred tax				$ 27,700
Excess tax benefits associated with vesting of share-based awards	$ 4,600	$ 1,700
Actual effective tax rate since tax effects of awards are treated as discrete item	10.70%	8.90%
Deferred tax assets, federal	$ 33,300			27,500
Deferred tax asset, state	21,500			18,200
ITC carryforward	$ 119,600			74,000
ITC carryforward, expiration period	20 years
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 95,100			78,700
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 371,900			310,600
Valuation allowance				$ 262
Scenario, Forecast
Operating Loss Carryforwards [Line Items]
Forecasted tax credits, net of deferred tax			$ 36,400