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Long-Term Debt And Lines of Credit (Narrative) (Details) - USD ($)
9 Months Ended
Sep. 30, 2019
Aug. 02, 2019
Jun. 20, 2018
Debt Instrument [Line Items]      
Standby letters of credit issued $ 37,900,000    
Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Borrowing amount   $ 450,000,000  
2018 Credit Agreement [Member] | Revolving Credit Facility [Member]      
Debt Instrument [Line Items]      
Revolving credit facility period, years 5 years    
Borrowing amount     $ 450,000,000
Amount outstanding $ 130,000,000.0    
Deferred financing costs 1,000,000.0    
Unused lines of credit $ 282,100,000    
2018 Credit Agreement [Member] | Revolving Credit Facility [Member] | LIBOR [Member]      
Debt Instrument [Line Items]      
Basis spread on variable interest rate 100.00%    
2018 Credit Agreement [Member] | Expansion Feature [Member]      
Debt Instrument [Line Items]      
Borrowing amount     $ 150,000,000