INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016
Operating Loss Carryforwards [Line Items]
Forecasted effective tax rate	8.70%	14.70%
Forecasted tax credits, net of deferred tax				$ 26,800
Excess tax benefits associated with vesting of share-based awards	$ 1,200	$ 1,600
Actual effective tax rate since tax effects of awards are treated as discrete item	5.50%	11.80%
Deferred tax assets, federal	$ 27,500			27,500
Deferred tax asset, state	19,000			$ 18,200
ITC carryforward, expiration period				20 years
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	78,700			$ 78,700
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	323,900			310,600
Valuation allowance	108			262
ITC carryforward	$ 79,100			$ 74,000
Scenario, Forecast
Operating Loss Carryforwards [Line Items]
Forecasted tax credits, net of deferred tax			$ 34,100