Employee Retirement Plans (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) agreement employee	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 1,070	$ 1,377	$ 1,685
Pre-tax accumulated other comprehensive loss - retirement benefit liability adjustment	(171)	(197)
Net liability	$ 1,241	$ 1,573
Number of employees | employee	2,022
Employees represented by unions through CBAs, percentage	11.00%
Number of CBA's to be negotiated | agreement	3
Number of CBA's | agreement	6
Company's maximum contribution percentage	5.00%
National Integrated Group Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
CBAs expiration date	Apr. 30, 2018