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Pension and Postretirement Plans (Narrative) (Details)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
USD ($)
Investment
companies
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
Investment
companies
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
Investment
Defined Benefit Plan Disclosure [Line Items]          
Special separation benefit expense     $ 0 $ 932  
Defined Benefit Pension Plan [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Special separation benefit expense $ 0 $ 932 $ 0 $ 932  
Percent of plan assets managed internally by the company     45.00%    
Percent of plan assets managed by investment companies     55.00%    
Number of investment companies actively managing plan assets | companies 2   2    
Percentage of total plan assets 100.00%   100.00%   100.00%
Defined Benefit Pension Plan [Member] | Separation Incentive Program [Member] | Forney [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Special separation benefit expense   $ 900      
Berkshire Hathaway Common Stock [Member] | Defined Benefit Pension Plan [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%    
Foreign Investments [Member] | Defined Benefit Pension Plan [Member] | Maximum [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Defined benefit plan, target allocation percentage of assets 23.00%   23.00%    
Fixed income securities [Member] | Defined Benefit Pension Plan [Member] | Minimum [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 Pension Plan [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 $ 1,154,400   $ 1,154,400   $ 1,079,300
Percentage of total plan assets 46.00%   46.00%   46.00%
Single Equity Concentration [Member] | Equity Securities [Member] | Defined Benefit Pension Plan [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 Pension Plan [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 Pension Plan [Member]          
Defined Benefit Plan Disclosure [Line Items]          
Minimum percentage of plan assets considered as significant concentrations in pension plans     10.00%   10.00%