Retirement Plans (Schedule of Costs of Retirement Plans) (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Contribution Plan Disclosure
Expenses associated with contributions made	$ 695	$ 694
United States
Defined Contribution Plan Disclosure
Expenses associated with contributions made	550	544
Canada
Defined Contribution Plan Disclosure
Expenses associated with contributions made	38	33
United Kingdom
Defined Contribution Plan Disclosure
Expenses associated with contributions made	$ 107	$ 117