Pension and Other Postretirement Benefits (Schedule of Total Expense for All Retirement Plans) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) plan	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Total retirement plan expense	$ 2,824	$ 2,572	$ 2,542
401(k) plan
Defined Benefit Plan Disclosure [Line Items]
Total retirement plan expense	2,403	2,031	1,876
Multiemployer and other defined benefit and pension plans
Defined Benefit Plan Disclosure [Line Items]
Total retirement plan expense	$ 70	195	239
Number of plans | plan	1
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Total retirement plan expense	$ 351	$ 346	$ 427