Retirement Plans (Schedule of Costs of Retirement Plans) (Details) - Pension Plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Contribution Plan Disclosure
Expenses associated with contributions made	$ 832	$ 902	$ 1,527	$ 1,596
United States
Defined Contribution Plan Disclosure
Expenses associated with contributions made	680	770	1,230	1,314
Canada
Defined Contribution Plan Disclosure
Expenses associated with contributions made	34	34	72	68
United Kingdom
Defined Contribution Plan Disclosure
Expenses associated with contributions made	$ 118	$ 98	$ 225	$ 214