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LONG-TERM DEBT / INTEREST EXPENSE (Details)
3 Months Ended 12 Months Ended
Aug. 10, 2015
USD ($)
day
$ / shares
Dec. 31, 2013
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Dec. 31, 2013
USD ($)
Sep. 30, 2013
USD ($)
Debt Instrument            
Draw on line of credit     $ 1,452,454,000 $ 1,342,378,000    
Term Loan Facility            
Debt Instrument            
Draw on line of credit     1,174,369,000 1,342,165,000    
Line of Credit | Revolving Credit Facility            
Debt Instrument            
Draw on line of credit     43,000,000 0    
Senior Credit Facility            
Debt Instrument            
Loss on debt refinancing     0 $ 0 $ 5,712,000  
Senior Credit Facility | Revolving Credit Facility            
Debt Instrument            
Line of credit facility, maximum borrowing capacity     $ 130,000,000      
Amended And Restated Senior Credit Facility            
Debt Instrument            
Effective interest rate     3.25% 3.25%    
Amended And Restated Senior Credit Facility | Revolving Credit Facility            
Debt Instrument            
Line of credit facility, maximum borrowing capacity           $ 80,000,000
Weighted average interest rate     2.60%      
Unused capacity for letters of credit, commitment fee percentage     0.50%      
Line of credit facility, remaining borrowing capacity     $ 85,900,000      
Amended And Restated Senior Credit Facility | Letter of Credit            
Debt Instrument            
Annual fee on outstanding letters of credit     2.50%      
Long-term line of credit     $ 1,100,000      
Amended And Restated Senior Credit Facility | Term Loan Facility            
Debt Instrument            
Proceeds from issuance of debt   $ 252,500,000        
Loss on debt refinancing   $ 5,700,000        
1.5% Convertible Senior Notes Due 2020 | Convertible senior notes            
Debt Instrument            
Effective interest rate     6.10%      
Draw on line of credit     $ 235,085,000 $ 0    
Debt instrument, principal $ 287,500,000.0   $ 287,500,000      
Debt instrument, interest rate, stated percentage 1.50%          
Convertible debt instrument, conversion ratio 0.0151156          
Convertible debt instrument conversion price (in dollars per share) | $ / shares $ 66.16          
Debt issuance costs, discounts and commissions $ 7,900,000          
Debt issuance costs, third party offering cost $ 300,000          
1.5% Convertible Senior Notes Due 2020 | Convertible senior notes | Debt Instrument, Redemption, Period One | Debt Instrument, Conversion, Option One            
Debt Instrument            
Convertible debt instrument, trading days threshold | day 20          
Convertible debt instrument percentage of stock price trigger threshold 130.00%          
Convertible debt instrument, consecutive trading days threshold 30 days          
1.5% Convertible Senior Notes Due 2020 | Convertible senior notes | Debt Instrument, Redemption, Period One | Debt Instrument, Conversion, Option Two            
Debt Instrument            
Convertible debt instrument, consecutive business days threshold 5 days          
Convertible debt instrument, consecutive trading days threshold 10 days          
Convertible debt instrument ratio of trading price per $1,000 in principal Amount 98.00%