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Debt and Finance Lease Obligations (Senior Credit Facility) (Details)
12 Months Ended 18 Months Ended
Jul. 16, 2019
USD ($)
Dec. 31, 2020
USD ($)
$ / shares
Dec. 31, 2019
USD ($)
$ / shares
Dec. 31, 2018
USD ($)
Jun. 30, 2020
Mar. 31, 2022
Dec. 31, 2021
Sep. 04, 2020
USD ($)
$ / shares
Line of Credit Facility [Line Items]                
Common shares, par value (in dollars per share) | $ / shares   $ 1.25 $ 1.25          
Repayments of debt   $ 191,258,000 $ 105,000,000 $ 60,000,000        
Revolving Credit Facility                
Line of Credit Facility [Line Items]                
Amount outstanding   0 0          
Current borrowing capacity   741,900,000 711,500,000          
Senior Credit Facility                
Line of Credit Facility [Line Items]                
Letters of credit, amount outstanding   $ 58,100,000 $ 88,500,000          
Revolving Credit Facility | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Maximum borrowing capacity $ 800,000,000.0              
Maximum increase in borrowing capacity 400,000,000.0              
Commitment fee percentage   0.20%            
Revolving Credit Facility | New Credit Agreement                
Line of Credit Facility [Line Items]                
Debt Instrument, Covenant, Maximum Amount Of Cash And Cash Equivalents Excluded From Leverage Ratio               $ 250,000,000.0
Common shares, par value (in dollars per share) | $ / shares               $ 1.25
Letter of Credit | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Maximum borrowing capacity 750,000,000.0              
Bridge Loan | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Maximum borrowing capacity $ 30,000,000.0              
London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Basis spread on variable rate 1.375%              
Base Rate | Revolving Credit Facility | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Basis spread on variable rate 0.375%              
Minimum | Revolving Credit Facility | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Unused capacity, commitment fee percentage 0.09%              
Minimum | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Basis spread on variable rate 1.00%              
Minimum | Base Rate | Revolving Credit Facility | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Basis spread on variable rate 0.00%              
Maximum | Revolving Credit Facility | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Unused capacity, commitment fee percentage 0.30%              
Maximum | Revolving Credit Facility | New Credit Agreement                
Line of Credit Facility [Line Items]                
Debt Instrument, Covenant, Percentage Of Dividends And Share Repurchases         115.00%      
Maximum | Revolving Credit Facility | New Credit Agreement | Forecast [Member]                
Line of Credit Facility [Line Items]                
Debt Instrument, Covenant, Leverage Ratio           4.00 4.00  
Debt Instrument, Covenant, Leverage Ratio With Acquisitions           4.50    
Maximum | London Interbank Offered Rate (LIBOR) | Revolving Credit Facility | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Basis spread on variable rate 1.75%              
Maximum | Base Rate | Revolving Credit Facility | New Senior Credit Facility                
Line of Credit Facility [Line Items]                
Basis spread on variable rate 0.75%