Commitments and Contingent Liabilities (Narrative) (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) tie	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014 USD ($) tie	Dec. 31, 2013 tie	Dec. 31, 2012 USD ($)	Dec. 31, 2017 USD ($)
Product Liability Contingency
Accrued warranty	$ 8,706						$ 8,682
Number of concrete ties manufactured | tie	3,000,000
Warranty period			10 years
Accrual for environmental loss	$ 6,134						6,144
Reserve for Concrete Ties
Product Liability Contingency
Accrued warranty	$ 7,630						$ 7,595
Warranty period						5 years
2005 Contract
Product Liability Contingency
Number of concrete ties manufactured ratio | tie	1.5
Period in which concrete ties will be replaced after sale	5 years
Warranty Policy
Product Liability Contingency
Warranty period						15 years
Warranty ratio						1
The UPRR
Product Liability Contingency
Number of concrete ties manufactured | tie	1,600,000
Warranty period						5 years
Warranty ratio						1.5
The 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 unreconciled warranty ties | tie				90,100
The UPRR | Warranty Policy
Product Liability Contingency
Number of ties manufactured that did not meet criteria to be covered as warranty replacement ties | tie					170,000