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Long-Term Debt - Summary (Details) - USD ($)
6 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Jun. 30, 2018
May 30, 2017
Debt Instrument [Line Items]        
Total long-term debt $ 636,222,000 $ 590,887,000 $ 517,060,000  
Deferred finance costs, net $ 3,800,000 4,100,000 4,400,000  
Debt ratio 2.25      
Senior notes 2024        
Debt Instrument [Line Items]        
Stated interest rate (percent)       5.375%
Face amount       $ 300,000,000.0
Line of Credit        
Debt Instrument [Line Items]        
Amount outstanding $ 340,000,000 295,000,000 221,500,000  
Maximum borrowing capacity 425,000,000.0      
Letters of credit outstanding, amount 3,700,000      
Remaining borrowing capacity $ 81,300,000      
Unused capacity, commitment fee (percent) 0.50%      
Interest rate at end of period (percent) 4.88%      
Net proceeds $ 45,000,000.0      
Line of Credit | 30-day LIBOR        
Debt Instrument [Line Items]        
Basis spread on variable rate (percent) 2.50%      
Line of Credit | Prime Rate        
Debt Instrument [Line Items]        
Basis spread on variable rate (percent) 1.50%      
Line of Credit | Minimum | 30-day LIBOR        
Debt Instrument [Line Items]        
Stated interest rate (percent) 0.00%      
Senior notes 2024        
Debt Instrument [Line Items]        
Total long-term debt $ 296,222,000 $ 295,887,000 $ 295,560,000  
Stated interest rate (percent) 5.375%