Postretirement Benefits - Fair Value Measurement for Pension Plan Assets by Major Category and Level of Input (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair value measurements of pension plan assets:
Total	$ 1,140,243	$ 1,081,061	$ 907,625
Employee pension plan | Qualified Plan | Funded Plan
Fair value measurements of pension plan assets:
Total	1,140,243	1,081,061
Employee pension plan | Qualified Plan | Funded Plan | Level 1
Fair value measurements of pension plan assets:
Total	153,205	147,397
Employee pension plan | Qualified Plan | Funded Plan | Level 2
Fair value measurements of pension plan assets:
Total	987,038	933,664
Employee pension plan | Qualified Plan | Funded Plan | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Qualified Plan | Funded Plan | Total equity securities
Fair value measurements of pension plan assets:
Total	506,389	493,595
Employee pension plan | Qualified Plan | Funded Plan | Total equity securities | Level 1
Fair value measurements of pension plan assets:
Total	139,688	134,841
Employee pension plan | Qualified Plan | Funded Plan | Total equity securities | Level 2
Fair value measurements of pension plan assets:
Total	366,701	358,754
Employee pension plan | Qualified Plan | Funded Plan | Total equity securities | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Qualified Plan | Funded Plan | U.S. equity securities
Fair value measurements of pension plan assets:
Total	305,440	296,624
Employee pension plan | Qualified Plan | Funded Plan | U.S. equity securities | Level 1
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Qualified Plan | Funded Plan | U.S. equity securities | Level 2
Fair value measurements of pension plan assets:
Total	305,440	296,624
Employee pension plan | Qualified Plan | Funded Plan | U.S. equity securities | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Qualified Plan | Funded Plan | Non-U.S. equity securities
Fair value measurements of pension plan assets:
Total	200,949	196,971
Employee pension plan | Qualified Plan | Funded Plan | Non-U.S. equity securities | Level 1
Fair value measurements of pension plan assets:
Total	139,688	134,841
Employee pension plan | Qualified Plan | Funded Plan | Non-U.S. equity securities | Level 2
Fair value measurements of pension plan assets:
Total	61,261	62,130
Employee pension plan | Qualified Plan | Funded Plan | Non-U.S. equity securities | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Qualified Plan | Funded Plan | Debt securities
Fair value measurements of pension plan assets:
Total	620,337	574,910
Employee pension plan | Qualified Plan | Funded Plan | Debt securities | Level 1
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Qualified Plan | Funded Plan | Debt securities | Level 2
Fair value measurements of pension plan assets:
Total	620,337	574,910
Employee pension plan | Qualified Plan | Funded Plan | Debt securities | Level 3
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Qualified Plan | Funded Plan | Other
Fair value measurements of pension plan assets:
Total	13,517	12,556
Employee pension plan | Qualified Plan | Funded Plan | Other | Level 1
Fair value measurements of pension plan assets:
Total	13,517	12,556
Employee pension plan | Qualified Plan | Funded Plan | Other | Level 2
Fair value measurements of pension plan assets:
Total	0	0
Employee pension plan | Qualified Plan | Funded Plan | Other | Level 3
Fair value measurements of pension plan assets:
Total	$ 0	$ 0