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Long-Term Debt (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Aug. 31, 2018
Nov. 01, 2016
Nov. 11, 2013
Debt Instrument [Line Items]          
Line of Credit Facility, Maximum Borrowing Capacity     $ 100,000,000.0 $ 175,000,000.0 $ 250,000,000.0
Allowable Amount for Issuance of Letters of Credit $ 30,000,000.0       $ 20,000,000.0
Debt Instrument, Covenant, Leverage Ratio 2        
Debt Covenant, Minimum Net Income Requirement $ 1.00        
Debt Instrument, Covenant minimum tangible net worth 250,000,000.0        
Long-term Line of Credit 0 $ 0      
Letters of Credit Outstanding on a Line of Credit, Amount Outstanding 11,500,000 11,300,000      
Line of Credit Facility, Remaining Borrowing Capacity $ 88,500,000 $ 88,700,000      
Prime Rate [Member]          
Debt Instrument [Line Items]          
Debt Instrument, Basis Spread on Variable Rate 0.00%        
Accordion Feature [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Maximum Borrowing Capacity $ 100,000,000.0        
Maximum [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Commitment Fee Percentage 0.175%        
Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]          
Debt Instrument [Line Items]          
Debt Instrument, Basis Spread on Variable Rate 0.90%        
Minimum [Member]          
Debt Instrument [Line Items]          
Line of Credit Facility, Commitment Fee Percentage 0.0725%        
Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]          
Debt Instrument [Line Items]          
Debt Instrument, Basis Spread on Variable Rate 0.70%