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Employee Postretirement Benefits - Allocation of Plan Assets (Details) - USD ($) $ in Thousands | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | $ 387,212 | $ 360,678
Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 374,415 | 351,458
Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
NAV |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 12,797 | 9,220
Equity Funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 149,479 | 180,169
Equity Funds | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 149,479 | 180,169
Equity Funds | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
Equity Funds | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
Fixed Income Funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 184,987 | 159,556
Fixed Income Funds | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 184,987 | 159,556
Fixed Income Funds | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
Fixed Income Funds | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
Hybrid Funds |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 11,776 | 11,729
Hybrid Funds | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 11,776 | 11,729
Hybrid Funds | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
Hybrid Funds | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
U.S. Treasury Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 28,173 |
U.S. Treasury Securities | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 28,173 |
U.S. Treasury Securities | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 |
U.S. Treasury Securities | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 |
SEI Energy Debt Collective Fund |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 12,797 | 9,220
SEI Energy Debt Collective Fund | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
SEI Energy Debt Collective Fund | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
SEI Energy Debt Collective Fund | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | 0 | 0
SEI Energy Debt Collective Fund | NAV |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets | $ 12,797 | 9,220
Cash Equivalents |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets |  | 4
Cash Equivalents | Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets |  | 4
Cash Equivalents | Level 2 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets |  | 0
Cash Equivalents | Level 3 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan Assets |  | $ 0

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