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DEBT - 1.00 CONVERTIBLE NOTES (Details)
3 Months Ended 9 Months Ended 12 Months Ended
Jul. 17, 2013
USD ($)
Jun. 18, 2013
USD ($)
label
$ / shares
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Mar. 31, 2017
USD ($)
Jul. 12, 2013
USD ($)
Convertible Notes                
Interest and other, net     $ 3,374,000 $ (3,715,000) $ (2,403,000) $ (15,298,000)    
1.00% Convertible Notes due 2018                
Convertible Notes                
Interest rate     1.00%   1.00%      
Estimated fair value of convertible notes     $ 72,227,000   $ 72,227,000      
Convertible Debt | 1.00% Convertible Notes due 2018                
Convertible Notes                
Principal amount at issuance   $ 250,000,000            
Interest rate   1.00%            
Percentage of par value at which debt was issued   98.50%            
Proceeds from issuance of debt $ 283,188,000 $ 246,250,000            
Period of overallotment option to purchase additional amount of debt granted to underwriters   30 days            
Amount pertaining to exercise of over-allotment of debt by underwriters $ 37,500,000              
Initial conversion rate of common stock per $1000 of principal amount of Convertible Notes (in shares)   46.4727            
Principal amount used for debt instrument conversion ratio   $ 1,000            
Initial conversion price of convertible notes into common stock (in dollars per share) | $ / shares   $ 21.52            
Number of shares to be converted into common stock | label   13,361,000            
Converted instrument amount     40,088,000   253,986,000      
Interest and other, net     700,000   4,900,000      
Estimated fair value of convertible notes               $ 225,567,000
Non-convertible borrowing rate 6.15%              
Carrying amount of the equity component of convertible notes               57,621,000
Banking, legal and accounting fees related to issuance of convertible notes               $ 2,815,000
Banking, legal and accounting fees related to issuance of convertible notes allocated to the liability component $ 2,209,000              
Banking, legal and accounting fees related to issuance of convertible notes allocated to the equity component $ 606,000              
Principal amount of Convertible Notes     14,163,000   14,163,000   $ 268,149,000  
The value by which Convertible Notes exceed the principal value         $ 58,064,000   $ 470,456,000  
Convertible Debt | 1.00% Convertible Notes due 2018 | Maximum                
Convertible Notes                
Additional amount of debt for purchase of which overallotment option is granted to underwriters   $ 37,500,000            
Convertible Debt | 1.00% Convertible Notes due 2018 | Conversion Terms at Holder's Option                
Convertible Notes                
Principal amount used for debt instrument conversion ratio   $ 1,000            
Target ratio of closing share price to conversion price as a condition for conversion or redemption of Convertible Notes (as a percent)   130.00%            
Ratio of closing share price to conversion price as a condition for conversion of Convertible Notes (as a percent)   98.00%            
Convertible Debt | 1.00% Convertible Notes due 2018 | Conversion Terms at Holder's Option | Minimum                
Convertible Notes                
Number of trading days triggering conversion of redemption feature   20 days            
Number of trading days in the measurement period that the entity's common stock closing price to conversion price must exceed a specified percentage of conversion price to trigger conversion feature of notes | label   5            
Convertible Debt | 1.00% Convertible Notes due 2018 | Conversion Terms at Holder's Option | Maximum                
Convertible Notes                
Number of trading days triggering conversion of redemption feature   30 days            
Number of trading days in the measurement period that the entity's common stock closing price to conversion price must exceed a specified percentage of conversion price to trigger conversion feature of notes | label   10            
Convertible Debt | 1.00% Convertible Notes due 2018 | Conversion Terms upon Occurrence of Certain Fundamental Company Changes                
Convertible Notes                
Percentage of principal amount for computation of redemption price   100.00%            
Convertible Debt | 1.00% Convertible Notes due 2018 | Conversion Terms, Event of Default                
Convertible Notes                
Minimum percentage of aggregate principal amount held by bondholders to declare notes due and payable   25.00%            
In event of default arising out of certain bankruptcy events, the percentage of principal amount due and payable   100.00%            
Convertible Debt | October 2017 Settlement Dates                
Convertible Notes                
Converted instrument amount     $ 2,000