Pensions and Other Postretirement Plans (Fair Value of Pension Plan Assets) (Details 9) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	$ 2,803,422	$ 2,312,706	$ 2,120,127
Cash equivalents and other short-term investments [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	199,873	237,132
U.S. equities [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	1,614,879	1,439,098
International equities [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	233,818	161,377
Private investment fund [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	496,458	151,854
U.S. stock index fund [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	256,291	322,229
Total investments [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	2,801,319	2,311,690
Receivables (Payables) for settlement of investments purchased, net [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	2,103	1,016
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	2,803,422	2,312,706
Level 1 [Member] | Cash equivalents and other short-term investments [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	2,218	2,133
Level 1 [Member] | U.S. equities [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	1,614,879	1,439,098
Level 1 [Member] | International equities [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	233,818	161,377
Level 1 [Member] | Private investment fund [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 1 [Member] | U.S. stock index fund [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 1 [Member] | Total investments [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	1,850,915	1,602,608
Level 2 [Member] | Cash equivalents and other short-term investments [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	197,655	234,999
Level 2 [Member] | U.S. equities [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 [Member] | International equities [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 [Member] | Private investment fund [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 [Member] | U.S. stock index fund [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 2 [Member] | Total investments [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	197,655	234,999
Level 3 [Member] | Cash equivalents and other short-term investments [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 3 [Member] | U.S. equities [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 3 [Member] | International equities [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	0	0
Level 3 [Member] | Private investment fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	496,458	151,854	0
Level 3 [Member] | Private investment fund [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	496,458	151,854
Level 3 [Member] | U.S. stock index fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	256,291	322,229	$ 601,395
Level 3 [Member] | U.S. stock index fund [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	256,291	322,229
Level 3 [Member] | Total investments [Member] | Fair Value, Recurring [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets at fair value	$ 752,749	$ 474,083