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LONG-TERM DEBT - 4.0 Percent Convertible Notes (Details) - Convertible Notes - 4.00% convertible notes due 2027
3 Months Ended 12 Months Ended
Jun. 30, 2015
Mar. 31, 2015
Sep. 30, 2017
USD ($)
trading_day
d
$ / shares
$ / note
shares
Sep. 22, 2017
USD ($)
Sep. 30, 2016
USD ($)
Feb. 28, 2007
USD ($)
Debt Instrument [Line Items]            
Stated interest rate     4.00%      
Debt instrument, face amount | $           $ 200,000,000
Equivalent shares of common stock per 1000 principal amount of convertible notes (in shares) | shares     37.4111      
Initial principal amount per note (in dollars per note) | $ / note     1,000      
Conversion price (in dollars per share) | $ / shares     $ 26.73      
Maximum number of common stock convertible notes are convertible into (in shares) | shares     1,000,000      
Redemption option price     100.00%      
Redemption price 5.00% 6.00% 100.00%      
Long-term debt | $     $ 24,000,000 $ 143,000,000 $ 142,000,000  
Triggering Event One            
Debt Instrument [Line Items]            
Threshold trading days | d     20      
Threshold consecutive trading days | trading_day     30      
Threshold percentage of stock price trigger     120.00%      
Triggering Event Two            
Debt Instrument [Line Items]            
Threshold trading days | d     5      
Threshold consecutive trading days | trading_day     5      
Threshold percentage of stock price trigger     97.00%