Annual report pursuant to Section 13 and 15(d)

Debt (Details)

v3.10.0.1
Debt (Details) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Dec. 13, 2018
Oct. 12, 2018
Dec. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Aug. 09, 2018
Jul. 13, 2018
Jun. 28, 2018
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     $ 1,220.8 $ 1,220.8 $ 437.4        
Current Maturities of Long-term Debt     (41.3) (41.3) (5.6)        
Long-Term Debt, Net     1,179.5 1,179.5 431.8        
Maturities of Long-term Debt [Abstract]                  
2019     41.3 41.3          
2020     41.4 41.4          
2021     338.1 338.1          
2022     35.8 35.8          
2023     302.8 302.8          
Thereafter     461.4 461.4          
Total Long-Term Debt Including Current Maturities     1,220.8 1,220.8 437.4        
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Maximum Borrowing Capacity     400.0 400.0          
Line of Credit Facility, Remaining Borrowing Capacity     396.1 396.1          
Letters of Credit Outstanding, Amount     4.8 $ 4.8          
Debt Instrument, Face Amount             $ 800.0    
Remaining Payment for Debt Extinguishment     115.0            
Payment for Debt Extinguishment or Debt Prepayment Cost     185.0            
Minimum [Member]                  
Line of Credit Facility [Abstract]                  
Debt Instrument, Covenant, Interest Coverage Ratio       3.00          
Maximum [Member]                  
Line of Credit Facility [Abstract]                  
Debt Instrument, Covenant, Leverage Ratio       3.50          
Senior Notes Due 2021 [Member]                  
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities [1]     $ 147.3 $ 147.3 148.2        
Interest Rate     4.625% 4.625%          
Due date       2021          
Discount on Long-term Debt     $ 0.0 $ 0.0 0.0        
Debt Issuance Costs, Net     1.0 1.0 1.5        
Maturities of Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities [1]     147.3 $ 147.3 148.2        
Line of Credit Facility [Abstract]                  
Debt Instrument, Redemption Price, Triggering Event       101.00%          
Term Loan Due 2021 [Member]                  
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities [2]     $ 149.5 $ 149.5 0.0        
Interest Rate     3.85% 3.85%          
Due date       2021          
Discount on Long-term Debt     $ 0.0 $ 0.0 0.0        
Debt Issuance Costs, Net     0.5 0.5 0.0        
Maturities of Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities [2]     149.5 149.5 0.0        
Debentures Due 2023 [Member]                  
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities [1]     $ 102.6 $ 102.6 103.4        
Interest Rate     7.375% 7.375%          
Due date       2023          
Discount on Long-term Debt     $ 0.1 $ 0.1 0.2        
Debt Issuance Costs, Net     0.2 0.2 0.2        
Maturities of Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities [1]     102.6 102.6 103.4        
Loan With Fond Du Lac County Economic Development Corporation Due 2021 [Member]                  
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     $ 15.3 $ 15.3 19.6        
Interest Rate     2.00% 2.00%          
Due date       2021          
Discount on Long-term Debt     $ 2.3 $ 2.3 3.0        
Debt Issuance Costs, Net     0.1 0.1 0.1        
Maturities of Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     15.3 15.3 19.6        
Line of Credit Facility [Abstract]                  
Total Loan Forgiveness       $ 2.1 $ 2.1 $ 2.1      
Annual Forgiveness Percent       43.00% 43.00% 43.00%      
Loan With Fond Du Lac County Economic Development Corporation Due 2021 [Member] | Maximum [Member]                  
Line of Credit Facility [Abstract]                  
Annual Forgiveness Percent       43.00%          
Notes Due 2027 [Member]                  
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     $ 162.5 $ 162.5 $ 162.4        
Interest Rate     7.125% 7.125%          
Due date       2027          
Discount on Long-term Debt     $ 0.3 $ 0.3 0.4        
Debt Issuance Costs, Net     0.4 0.4 0.4        
Maturities of Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     162.5 162.5 162.4        
Notes Payable Through 2028 [Member]                  
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     $ 6.9 $ 6.9 3.8        
Interest Rate     5.892% 5.892%          
Due date       2028          
Discount on Long-term Debt     $ 0.2 $ 0.2 0.2        
Debt Issuance Costs, Net     0.0 0.0 0.0        
Maturities of Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     6.9 6.9 3.8        
Senior Notes Due 2048 [Member] [Member]                  
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     $ 176.5 $ 176.5 0.0        
Interest Rate     6.50% 6.50%          
Due date       2048          
Discount on Long-term Debt     $ 0.0 $ 0.0 0.0        
Debt Issuance Costs, Net     8.5 8.5 0.0        
Maturities of Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     176.5 $ 176.5 0.0        
Line of Credit Facility [Abstract]                  
Debt Instrument, Redemption Price, Triggering Event       101.00%          
Term Loan Due 2023 [Member]                  
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities [3],[4]     $ 339.7 $ 339.7 0.0        
Interest Rate     4.10% 4.10%          
Due date       2023          
Discount on Long-term Debt     $ 0.0 $ 0.0 0.0        
Debt Issuance Costs, Net     1.6 1.6 0.0        
Maturities of Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities [3],[4]     339.7 339.7 0.0        
Senior Notes Due 2049 [Member]                  
Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     $ 120.5 $ 120.5 0.0        
Interest Rate     6.625% 6.625%          
Due date       2049          
Discount on Long-term Debt     $ 0.0 $ 0.0 0.0        
Debt Issuance Costs, Net     4.5 4.5 0.0        
Maturities of Long-term Debt [Abstract]                  
Total Long-Term Debt Including Current Maturities     120.5 $ 120.5 $ 0.0        
Line of Credit Facility [Abstract]                  
Debt Instrument, Redemption Price, Triggering Event       101.00%          
Unsecured Debt [Member]                  
Line of Credit Facility [Abstract]                  
Debt Instrument, Face Amount             800.0    
Bridge Loan [Member] | Unsecured Debt [Member]                  
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Maximum Borrowing Capacity                 $ 1,100.0
Bridge Facility, Line of Credit Amount Terminated               $ 300.0  
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases               $ 800.0  
Line of Credit [Member]                  
Line of Credit Facility [Abstract]                  
Letters of Credit Outstanding, Amount     $ 3.9 $ 3.9          
Line of Credit Facility, Increase (Decrease), Other, Net       $ 100.0          
Line of Credit Facility, Commitment Fee Percentage       0.15%          
Line of Credit [Member] | Minimum [Member]                  
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Commitment Fee Percentage       0.125%          
Line of Credit [Member] | Maximum [Member]                  
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Commitment Fee Percentage       0.35%          
Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member]                  
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Interest Rate During Period       1.10%          
Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]                  
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Interest Rate During Period       1.00%          
Line of Credit [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]                  
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Interest Rate During Period       1.90%          
Line of Credit [Member] | Base Rate [Member]                  
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Interest Rate During Period       0.10%          
Line of Credit [Member] | Base Rate [Member] | Minimum [Member]                  
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Interest Rate During Period       0.00%          
Line of Credit [Member] | Base Rate [Member] | Maximum [Member]                  
Line of Credit Facility [Abstract]                  
Line of Credit Facility, Interest Rate During Period       0.90%          
Senior Notes Due 2048 [Member] [Member] | Unsecured Debt [Member]                  
Line of Credit Facility [Abstract]                  
Debt Instrument, Face Amount   $ 185.0              
Proceeds from Issuance of Debt   $ 176.5              
Term Loan Due 2023 [Member] | Unsecured Debt [Member]                  
Line of Credit Facility [Abstract]                  
Debt Instrument, Face Amount             350.0    
364 Day Tranche Loan [Member] | Unsecured Debt [Member]                  
Line of Credit Facility [Abstract]                  
Debt Instrument, Face Amount             300.0    
Senior Notes Due 2049 [Member] | Unsecured Debt [Member]                  
Line of Credit Facility [Abstract]                  
Debt Instrument, Face Amount $ 125.0                
Proceeds from Issuance of Debt $ 120.5                
Term Loan Due 2021 [Member] | Unsecured Debt [Member]                  
Line of Credit Facility [Abstract]                  
Debt Instrument, Face Amount             $ 150.0    
[1] Included in Senior notes, 4.625 percent due 2021 and Debentures, 7.375 percent due 2023 at December 31, 2018 and December 31, 2017, are the aggregate fair values related to the fixed-to-floating interest rate swaps as discussed in Note 15 – Financial Instruments.
[2] As of December 31, 2018, the interest rate was 3.85%
[3] As of December 31, 2018, the interest rate was 4.10%.
[4] Beginning in December 2018, scheduled repayment of the 5-year term loan occurs each March, June, September and December equal to 2.50% of the aggregate principal amount of $350.0 million. The remaining principal amount is due August 2023.