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Taxes on Income, Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Deferred tax assets [Abstract]    
Compensated absences $ 432 $ 739
Allowance for doubtful accounts 1,875 2,534
Postretirement health care benefits 1,190 2,234
Insurance accruals 4,599 9,128
Deferred compensation 1,849 11,124
Unrealized loss on defined benefit plans 11,097 28,832
Operating loss carryforwards 15,540 7,846
Pension benefits 549 0
Other 18,474 25,735
Deferred tax assets, gross 55,605 88,172
Valuation allowances (15,308) (7,417)
Deferred tax assets, net of valuation allowance 40,297 80,755
Deferred tax liabilities [Abstract]    
Property (428,947) (654,751)
Deferred state taxes (58,366) (54,812)
Pension benefits 0 (2,799)
Goodwill and other intangibles (9,015) (51,551)
Other (12,420) (22,295)
Deferred tax liabilities (508,748) (786,208)
Net deferred tax liabilities (468,451) $ (705,453)
Operating Loss Carryforwards [Line Items]    
Operating loss carryforwards, net of valuation allowance $ 232  
Expiration dates, operating loss carryforwards Dec. 31, 2030  
Unrecognized tax benefits including interest and penalties $ 2,462  
Amount that would impact the effective tax rate, if recognized 1,947  
Canada [Member]    
Operating Loss Carryforwards [Line Items]    
Operating loss carryforwards $ 6,019  
Expiration dates, operating loss carryforwards Dec. 31, 2038  
State and Local Jurisdiction [Member] | Minimum [Member]    
Income Tax Examination [Line Items]    
Years open to audit under the statute of limitations 2011  
State and Local Jurisdiction [Member] | Maximum [Member]    
Income Tax Examination [Line Items]    
Years open to audit under the statute of limitations 2016  
Internal Revenue Service (IRS) [Member] | Minimum [Member]    
Income Tax Examination [Line Items]    
Years open to audit under the statute of limitations 2014  
Internal Revenue Service (IRS) [Member] | Maximum [Member]    
Income Tax Examination [Line Items]    
Years open to audit under the statute of limitations 2016