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Other Employee Benefit Plans (Narrative) (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Matching contribution (as a percent) 6.00%    
Discretionary contribution to plan $ 0 $ 10,445,000 $ 0
Payments and costs of plan $ 10,737,000 20,655,000 9,888,000
Minimum      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Discretionary matching contribution (as a percent) 1.00%    
Maximum      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Discretionary matching contribution (as a percent) 6.00%    
Retiree Health Benefit Act of 1992      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Contributions to multi-employer plan $ 6,042,000 6,829,000 7,647,000
Combined fund obligation 62,295,000    
Multiemployer Plans      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Letters of credit outstanding 18,669,000 19,860,000 $ 20,983,000
Long-Term Disability      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Combined total obligation $ 12,749,000 $ 12,022,000