XML 107 R92.htm IDEA: XBRL DOCUMENT v3.20.4
Savings Plans, Pension Plans and Other Postretirement Employee Benefits (Narrative) (Details) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Feb. 29, 2020
Mar. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2009
Defined Benefit Plan Disclosure [Line Items]            
Contributions by employer     $ 3,600,000 $ 3,900,000 $ 3,700,000  
Accumulated benefit obligation     390,300,000 458,100,000    
Funding of pension and other postretirement benefit plans     10,004,000 5,678,000 $ 57,580,000  
Level 3 [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Investments in Level 3     0 $ 0    
Qualified Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Pension plan and other postretirement employee benefit, estimated payments in next fiscal year     $ 1,800,000      
Accumulated Other Comprehensive Loss [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Decrease in accumulated postretirement benefit obligations           $ 76,700,000
Management Deferred Compensation Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Annual incentive plan, employee permitted minimum defer percentage     50.00%      
Annual incentive plan, employee permitted maximum defer percentage     100.00%      
Management Deferred Compensation Plan [Member] | Minimum [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Basic salary defer percentage     50.00%      
Pension Plans [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Change in monthly retirement benefit amount $ 0          
Non-cash pretax settlement charge 43,000,000.0          
Pension plan and other postretirement employee benefit, estimated payments in next fiscal year     $ 21,923,000      
Pension Plans [Member] | Qualified Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Discount rate used to measure projected benefit obligations for qualified pension plans     2.95% 3.40%    
Pension Plans [Member] | Qualified Plan [Member] | Funded with Plan Assets [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Transfer of outstanding pension benefit obligation related to qualified pension plans to insurance company $ 101,100,000          
Reduction in funded status of qualified pension plans   $ 26,200,000        
Pension Plans [Member] | Nonqualified Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Pension plan and other postretirement employee benefit, estimated payments in next fiscal year     $ 2,400,000      
Other Postretirement Benefit Plans [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Pension plan and other postretirement employee benefit, estimated payments in next fiscal year     4,211,000      
Other Postretirement Benefit Plans [Member] | Nonqualified Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Pension plan and other postretirement employee benefit, estimated payments in next fiscal year     $ 4,200,000      
Non Deltic Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Defined Benefit Plan, Assumption Health Care Cost Trend Rate for Next Fiscal Year     4.50%      
Non Deltic Plan [Member] | Minimum [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Health care cost trend rate assumed for next fiscal year     6.36%      
Non Deltic Plan [Member] | Maximum [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Health care cost trend rate assumed for next fiscal year     7.05%      
Deltic Plan [Member]            
Defined Benefit Plan Disclosure [Line Items]            
Health care cost trend rate assumed for next fiscal year     6.78%      
Defined Benefit Plan, Assumption Health Care Cost Trend Rate for Next Fiscal Year     4.50%