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Pension and Postretirement Plans (Narrative) (Details) - Defined Benefit Pension Plan [Member]
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
USD ($)
Investment
companies
Jun. 30, 2018
USD ($)
Jun. 30, 2019
USD ($)
Investment
companies
Jun. 30, 2018
USD ($)
Dec. 31, 2018
USD ($)
Investment
Defined Benefit Plan Disclosure [Line Items]          
Special separation benefit expense $ 6,607 $ 0 $ 6,607 $ 0  
Percent of plan assets managed internally by the company     44.00%    
Percent of plan assets managed by investment companies     56.00%    
Number of investment companies actively managing plan assets | companies 2   2    
Percentage of total plan assets 100.00%   100.00%   100.00%
Berkshire Hathaway Common Stock [Member] | Investment Manager 2 [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator     20.00%    
Alphabet and Berkshire Hathaway Common Stock [Member] | Investment Manager 1 [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator     15.00%    
Foreign Investments [Member] | Maximum [Member] | Investment Manager 1 [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Defined benefit plan, target allocation percentage of assets 25.00%   25.00%    
Foreign Investments [Member] | Maximum [Member] | Investment Manager 2 [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Defined benefit plan, target allocation percentage of assets 15.00%   15.00%    
Fixed income securities [Member] | Minimum [Member] | Investment Manager 1 [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Defined benefit plan, target allocation percentage of assets 5.00%   5.00%    
Fixed income securities [Member] | Minimum [Member] | Investment Manager 2 [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Defined benefit plan, target allocation percentage of assets 10.00%   10.00%    
Single Equity Concentration [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Defined benefit plan, target allocation maximum percentage of assets, singular equity security, without prior approval by plan administrator     10.00%    
Value of investments $ 1,000,100   $ 1,000,100   $ 945,600
Percentage of total plan assets 41.00%   41.00%   45.00%
Single Equity Concentration [Member] | Equity Securities [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Number of investments the company's pension plan held which individually exceed 10% of total plan assets | Investment 1   1   1
Single Equity Concentration [Member] | Equity Funds [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Number of investments the company's pension plan held which individually exceed 10% of total plan assets | Investment 1   1   1
Concentration In Single Entity, Type Of Industry, Foreign Country Or Individual Fund [Member] | Defined Benefit Plan Assets Total [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Minimum percentage of plan assets considered as significant concentrations in pension plans     10.00%   10.00%
Education [Member] | Separation Incentive Program [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Special separation benefit expense $ 6,600