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Pension and Other Postretirement Benefits (Schedule of Total Expense for All Retirement Plans) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]      
Total retirement plan expense $ 2,927 $ 3,044 $ 2,887
Defined benefit pension plan      
Defined Benefit Plan Disclosure [Line Items]      
Total retirement plan expense 4 28 52
401(k) plan      
Defined Benefit Plan Disclosure [Line Items]      
Total retirement plan expense 2,262 2,248 1,952
Other Postretirement Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Total retirement plan expense 427 476 587
Multiemployer defined benefit plans      
Defined Benefit Plan Disclosure [Line Items]      
Total retirement plan expense $ 234 $ 292 $ 296