Retirement Plans (Schedule of Costs of Retirement Plans) (Details) - Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure
Expenses associated with contributions made	$ 3,406	$ 3,314
United States
Defined Contribution Plan Disclosure
Expenses associated with contributions made	2,762	2,641
Canada
Defined Contribution Plan Disclosure
Expenses associated with contributions made	193	223
United Kingdom
Defined Contribution Plan Disclosure
Expenses associated with contributions made	$ 451	$ 450