Retirement Plans (Narrative) (Details) - Pension Plan $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) plan
Defined Benefit Plan Disclosure
Defined contribution plan, number	6
United States
Defined Benefit Plan Disclosure
Number of retirement plans	3
Defined benefit plan, number	1
Defined contribution plan, number	2
Canada
Defined Benefit Plan Disclosure
Post-retirement benefit plan number	1
Defined contribution plan, number	2
United Kingdom
Defined Benefit Plan Disclosure
Defined benefit plan, number	1
Defined contribution plan, number	2
Defined benefit plans, estimated future employer contributions in current fiscal year | $	$ 262
Defined benefit plan, contributions by employer | $	$ 65