Commitments and Contingent Liabilities (Narrative) (Details) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2014	Jun. 30, 2018 USD ($) tie	Dec. 31, 2015	Dec. 31, 2014 USD ($) tie	Dec. 31, 2013 tie	Dec. 31, 2012 USD ($)	Dec. 31, 2017 USD ($)
Product Liability Contingency
Accrued warranty | $		$ 8,705					$ 8,682
Number of concrete ties manufactured | tie		3,000,000
Warranty period			10 years
Number of Concrete Ties Excluded from Warranty | tie				90,100
Accrual for environmental loss | $		$ 6,144					6,144
Reserve for concrete ties
Product Liability Contingency
Accrued warranty | $		$ 7,668					$ 7,595
Warranty period						5 years
2005 Contract
Product Liability Contingency
Number of concrete ties manufactured ratio | tie		1.5
Warranty policy
Product Liability Contingency
Warranty period						15 years
Warranty Ratio						1
Uprr
Product Liability Contingency
Number of concrete ties manufactured | tie		1,600,000
Warranty period						5 years
Warranty Ratio						1.5
Uprr | Reserve for concrete ties
Product Liability Contingency
Litigation settlement amount | $						$ 12,000
Product warranty expense | $						$ 22,000
Cure period to claim	90 days				90 days
Change in standard product warranty accrual | $				$ 8,766
Number of Concrete Ties Excluded from Warranty | tie				90,100
Uprr | Warranty policy
Product Liability Contingency
Ties manufactured that did not meet criteria to be covered as warranty replacement ties | tie					170,000