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Debt (Additional Information) (Details) - USD ($)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Debt Instrument [Line Items]              
Interest expense incurred on outstanding debt $ 2,100,000 $ 1,100,000 $ 4,200,000 $ 2,000,000.0      
Borrowings under revolving credit facility $ 195,482,000   $ 195,482,000   $ 228,482,000    
Debt instrument, leverage ratio, maximum 2.75   2.75        
Maximum              
Debt Instrument [Line Items]              
Dividends     $ 20,000,000.0        
Credit Agreement              
Debt Instrument [Line Items]              
Variable rate lower range basis spread 37.50%   37.50%        
Variable rate higher range basis spread 75.00%   75.00%        
Third Amended Credit Agreement              
Debt Instrument [Line Items]              
Leverage ratio 3.25   3.25        
One-time leverage ratio maximum option 3.50   3.50        
ICR covenant limit 3.00   3.00        
Discretionary principal payments on revolving credit facility     $ 33,000,000.0        
Outstanding borrowings $ 1,400,000   $ 1,400,000        
Eurocurrency loans | Credit Agreement              
Debt Instrument [Line Items]              
Line of credit, LIBOR rate, minimum spread 137.50%   137.50%        
Line of credit, LIBOR rate, maximum spread 175.00%   175.00%        
Revolving Credit Facility | Third Amended Credit Agreement              
Debt Instrument [Line Items]              
Debt instrument, term           5 years  
Maximum borrowing capacity           $ 450,000,000.0 $ 450,000,000.0
Additional borrowing capacity           $ 175,000,000.0  
Revolving Credit Facility | Third Amended Credit Agreement | Minimum              
Debt Instrument [Line Items]              
Unused capacity, commitment fee percentage     20.00%        
Revolving Credit Facility | Third Amended Credit Agreement | Maximum              
Debt Instrument [Line Items]              
Unused capacity, commitment fee percentage     30.00%        
Interest rate swap | Revolving Credit Facility | Third Amended Credit Agreement              
Debt Instrument [Line Items]              
Hedged balance on debt instrument             $ 75,000,000.0
Griswold              
Debt Instrument [Line Items]              
Proceeds from line of credit         82,500,000    
Rogers Plan              
Debt Instrument [Line Items]              
Additional borrowing under line of credit         $ 20,000,000.0    
Federal Funds Rate | Credit Agreement              
Debt Instrument [Line Items]              
Basis spread on variable rate     0.50%        
London Interbank Offered Rate (LIBOR) | Third Amended Credit Agreement              
Debt Instrument [Line Items]              
Basis spread on variable rate     1.50%