Pensions and Other Postretirement Benefit Plans (Schedule of Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 239,051	$ 211,755	$ 178,942
Pension plans | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	239,051	211,755
Pension plans | Fair Value, Inputs, Level 1 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,095	3,009
Pension plans | Fair Value, Inputs, Level 2 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	104,642	92,721
Pension plans | Fair Value, Inputs, Level 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,819	3,244
Pension plans | Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	109,556	98,974
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	0
Common Stocks and equity funds | Pension plans | Fair Value, Inputs, Level 1 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	216
Common Stocks and equity funds | Pension plans | Fair Value, Inputs, Level 2 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common Stocks and equity funds | Pension plans | Fair Value, Inputs, Level 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common Stocks and equity funds | Pension plans | Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	216
Common Stocks and equity funds | Pension plans | Fair Value Measured at Net Asset Value Per Share | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,213	56,846
Debt securities | Pension plans | Fair Value, Inputs, Level 1 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Debt securities | Pension plans | Fair Value, Inputs, Level 2 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	104,642	92,721
Debt securities | Pension plans | Fair Value, Inputs, Level 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Debt securities | Pension plans | Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	104,642	92,721
Insurance contracts | Pension plans | Fair Value, Inputs, Level 1 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Insurance contracts | Pension plans | Fair Value, Inputs, Level 2 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Insurance contracts | Pension plans | Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,819	3,244	$ 2,890
Insurance contracts | Pension plans | Fair Value, Inputs, Level 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,819	3,244
Insurance contracts | Pension plans | Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,819	3,244
Cash and short-term investments | Pension plans | Fair Value, Inputs, Level 1 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,095	2,793
Cash and short-term investments | Pension plans | Fair Value, Inputs, Level 2 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and short-term investments | Pension plans | Fair Value, Inputs, Level 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Cash and short-term investments | Pension plans | Fair Value, Inputs, Level 1, 2 and 3 | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,095	2,793
Fixed income funds | Pension plans | Fair Value Measured at Net Asset Value Per Share | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	107,012	52,751
Limited partnerships | Pension plans | Fair Value Measured at Net Asset Value Per Share | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,270	$ 3,184