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Long-Term Debt (Details)
3 Months Ended 6 Months Ended
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
May 30, 2017
USD ($)
Debt Instrument [Line Items]            
Total long-term debt $ 517,060,000 $ 391,804,000 $ 517,060,000 $ 391,804,000 $ 402,243,000  
Deferred finance costs, net $ 4,400,000 5,200,000 $ 4,400,000 5,200,000 4,800,000  
Debt ratio 2.25   2.25      
Loss on extinguishment of debt $ 0 (14,094,000) $ 0 (14,094,000)    
Line of Credit | 2016 Credit Facility            
Debt Instrument [Line Items]            
Amount outstanding 221,500,000 97,000,000 221,500,000 97,000,000 107,000,000  
Maximum borrowing capacity 400,000,000   400,000,000      
Letters of credit outstanding, amount 5,100,000   5,100,000      
Remaining borrowing capacity $ 173,400,000   $ 173,400,000      
Unused capacity, commitment fee percentage     0.50%      
Interest rate at end of period (percent) 4.50%   4.50%      
Net proceeds     $ 114,500,000      
Line of Credit | 2016 Credit Facility | 30-day LIBOR            
Debt Instrument [Line Items]            
Basis spread on variable rate (percent)     2.50%      
Line of Credit | 2016 Credit Facility | Prime Rate            
Debt Instrument [Line Items]            
Basis spread on variable rate (percent)     1.50%      
Line of Credit | Minimum | 2016 Credit Facility | 30-day LIBOR            
Debt Instrument [Line Items]            
Stated interest rate (percent) 0.00%   0.00%      
Senior notes 2024            
Debt Instrument [Line Items]            
Stated interest rate (percent)           5.375%
Face amount           $ 300,000,000
Senior notes 2021            
Debt Instrument [Line Items]            
Stated interest rate (percent)           6.75%
Face amount           $ 200,000,000
Senior notes 2024            
Debt Instrument [Line Items]            
Stated interest rate (percent) 5.375%   5.375%      
Unamortized debt issuance costs $ 295,560,000 $ 294,804,000 $ 295,560,000 $ 294,804,000 $ 295,243,000  
Senior notes 2021            
Debt Instrument [Line Items]            
Stated interest rate (percent) 6.75%   6.75%