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Long-Term Debt And Lines of Credit (Narrative) (Details) - USD ($)
12 Months Ended
Jun. 20, 2018
Dec. 31, 2019
Dec. 31, 2018
Aug. 02, 2019
Revolving Credit Facility [Member]        
Debt Instrument [Line Items]        
Borrowing amount       $ 450,000,000
2018 Credit Agreement [Member]        
Debt Instrument [Line Items]        
Standby letters of credit issued   $ 37,900,000    
2018 Credit Agreement [Member] | LIBOR [Member]        
Debt Instrument [Line Items]        
Basis spread on variable interest rate   1.00% 1.00%  
2018 Credit Agreement [Member] | Revolving Credit Facility [Member]        
Debt Instrument [Line Items]        
Revolving credit facility period, years 5 years      
Borrowing amount $ 450,000,000      
Deferred financing costs   $ 1,000,000.0    
Unused lines of credit   $ 322,100,000    
2018 Credit Agreement [Member] | Expansion Feature [Member]        
Debt Instrument [Line Items]        
Borrowing amount $ 150,000,000