Pensions and Other Postretirement Benefit Plans (Schedule of Fair Value of Plan Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other postretirement benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	211,755	178,942	$ 205,586
Pension Plans [Member] | Total investments in the fair value hierarchy [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	98,974	84,713
Pension Plans [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,009	3,300
Pension Plans [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	92,721	78,523
Pension Plans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,244	2,890
Common Stocks and Equity Funds [Member] | Other postretirement benefits [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	216	284
Common Stocks and Equity Funds [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	216	284
Investment of plan assets	56,846	42,852
Common Stocks and Equity Funds [Member] | Pension Plans [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Common Stocks and Equity Funds [Member] | Pension Plans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Debt Securities [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	92,721	78,523
Debt Securities [Member] | Pension Plans [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Debt Securities [Member] | Pension Plans [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	92,721	78,523
Debt Securities [Member] | Pension Plans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Fixed income funds [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment of plan assets	52,751	47,534
Insurance Contracts [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,244	2,890
Insurance Contracts [Member] | Pension Plans [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Insurance Contracts [Member] | Pension Plans [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Insurance Contracts [Member] | Pension Plans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,244	2,890
Cash and Short-Term Investments [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,793	3,016
Cash and Short-Term Investments [Member] | Pension Plans [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,793	3,016
Cash and Short-Term Investments [Member] | Pension Plans [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Cash and Short-Term Investments [Member] | Pension Plans [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Limited Partnerships [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment of plan assets	3,184	3,843
Hedge Funds [Member] | Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Investment of plan assets	$ 211,755	$ 178,942