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Credit Facilities and Long-Term Debt, Revolving Credit Facility (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
JPMorgan Chase Bank Credit Facility [Member]    
Line of Credit Facility [Abstract]    
Maximum borrowing capacity $ 250,000  
Line of credit facility, additional borrowing capacity $ 50,000  
Maturity date Dec. 31, 2023  
Additional available borrowing capacity $ 203,100  
Outstanding borrowings under credit facility $ 43,700 $ 57,000
Weighted average interest rate 3.90% 2.70%
JPMorgan Chase Bank Credit Facility [Member] | LIBOR [Member] | Minimum [Member]    
Line of Credit Facility [Abstract]    
Margin on variable rate 1.25%  
JPMorgan Chase Bank Credit Facility [Member] | LIBOR [Member] | Maximum [Member]    
Line of Credit Facility [Abstract]    
Margin on variable rate 1.75%  
JPMorgan Chase Bank Credit Facility [Member] | Alternate Base Rate [Member]    
Line of Credit Facility [Abstract]    
Outstanding borrowings under credit facility $ 3,700  
Weighted average interest rate 5.80%  
Average daily loan balance outstanding $ 1,800 $ 3,800
JPMorgan Chase Bank Credit Facility [Member] | Alternate Base Rate [Member] | Minimum [Member]    
Line of Credit Facility [Abstract]    
Margin on variable rate 0.25%  
JPMorgan Chase Bank Credit Facility [Member] | Alternate Base Rate [Member] | Maximum [Member]    
Line of Credit Facility [Abstract]    
Margin on variable rate 0.75%  
JPMorgan Chase Bank Credit Facility [Member] | Fixed Assets Included in Borrowing Base [Member] | Maximum [Member]    
Line of Credit Facility [Abstract]    
Borrowing base $ 25,000  
Borrowing base percentage 10.00%  
JPMorgan Chase Bank Credit Facility [Member] | Fixed Assets Not Included in Borrowing Base [Member]    
Line of Credit Facility [Abstract]    
Borrowing base $ 31,250  
Borrowing base percentage 12.50%  
JPMorgan Chase Bank Credit Facility [Member] | Direct Borrowings [Member]    
Line of Credit Facility [Abstract]    
Outstanding borrowings under credit facility $ 40,000  
Weighted average interest rate 3.40%  
Line of Credit [Member]    
Line of Credit Facility [Abstract]    
Coverage ratio 1  
Line of Credit [Member] | Pay Cash Dividend [Member]    
Line of Credit Facility [Abstract]    
Agreement permissions $ 20,000  
Line of Credit [Member] | Stock Repurchase [Member]    
Line of Credit Facility [Abstract]    
Agreement permissions 20,000  
Line of Credit [Member] | Stock Repurchase [Member] | Minimum [Member]    
Line of Credit Facility [Abstract]    
Borrowing base 25,000  
Line of Credit [Member] | Cash Dividend And Stock Repurchases [Member] | Minimum [Member]    
Line of Credit Facility [Abstract]    
Agreement permissions 20,000  
Line of Credit [Member] | CANADA [Member]    
Line of Credit Facility [Abstract]    
Maximum borrowing capacity $ 10,000