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Fair value measurements - Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Assets |  |
Total postretirement benefit plan assets | $ 265,875 | $ 431,047
Common collective trust |  |
Assets |  |
Total postretirement benefit plan assets | 6,497 | 8,882
Mutual funds |  |
Assets |  |
Total postretirement benefit plan assets | 50,467 | 118,559
Fixed income securities |  |
Assets |  |
Total postretirement benefit plan assets | 198,628 | 292,883
Short-term investments |  |
Assets |  |
Total postretirement benefit plan assets | 1,099 | 1,211
Real estate funds |  |
Assets |  |
Total postretirement benefit plan assets | 680 | 592
Cash and accrued income |  |
Assets |  |
Total postretirement benefit plan assets | 8,504 | 8,920
Derivatives designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | (172) | 1,491
Derivatives designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | (863) | (121)
Derivatives not designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | (8,638) | 683
Derivatives not designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | (54) | (41)
Derivatives not designated as hedging instruments | Interest Rate Lock Contract |  |
Assets |  |
Derivatives, net |  | (550)
Assets measured at NAV |  |
Assets |  |
Total postretirement benefit plan assets | 40,104 | 50,594
Assets measured at NAV | Common collective trust |  |
Assets |  |
Total postretirement benefit plan assets | 6,497 | 8,882
Assets measured at NAV | Mutual funds |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Assets measured at NAV | Fixed income securities |  |
Assets |  |
Total postretirement benefit plan assets | 32,927 | 41,120
Assets measured at NAV | Short-term investments |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Assets measured at NAV | Real estate funds |  |
Assets |  |
Total postretirement benefit plan assets | 680 | 592
Assets measured at NAV | Cash and accrued income |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Assets measured at NAV | Derivatives designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Assets measured at NAV | Derivatives designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Assets measured at NAV | Derivatives not designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Assets measured at NAV | Derivatives not designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Assets measured at NAV | Derivatives not designated as hedging instruments | Interest Rate Lock Contract |  |
Assets |  |
Derivatives, net |  | 0
Level 1 |  |
Assets |  |
Total postretirement benefit plan assets | 8,504 | 8,920
Level 1 | Common collective trust |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 1 | Mutual funds |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 1 | Fixed income securities |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 1 | Short-term investments |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 1 | Real estate funds |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 1 | Cash and accrued income |  |
Assets |  |
Total postretirement benefit plan assets | 8,504 | 8,920
Level 1 | Derivatives designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Level 1 | Derivatives designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Level 1 | Derivatives not designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Level 1 | Derivatives not designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Level 1 | Derivatives not designated as hedging instruments | Interest Rate Lock Contract |  |
Assets |  |
Derivatives, net |  | 0
Level 2 |  |
Assets |  |
Total postretirement benefit plan assets | 217,267 | 371,533
Level 2 | Common collective trust |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 2 | Mutual funds |  |
Assets |  |
Total postretirement benefit plan assets | 50,467 | 118,559
Level 2 | Fixed income securities |  |
Assets |  |
Total postretirement benefit plan assets | 165,701 | 251,763
Level 2 | Short-term investments |  |
Assets |  |
Total postretirement benefit plan assets | 1,099 | 1,211
Level 2 | Real estate funds |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 2 | Cash and accrued income |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 2 | Derivatives designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | (172) | 1,491
Level 2 | Derivatives designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | (863) | (121)
Level 2 | Derivatives not designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | (8,638) | 683
Level 2 | Derivatives not designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | (54) | (41)
Level 2 | Derivatives not designated as hedging instruments | Interest Rate Lock Contract |  |
Assets |  |
Derivatives, net |  | (550)
Level 3 |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 3 | Common collective trust |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 3 | Mutual funds |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 3 | Fixed income securities |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 3 | Short-term investments |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 3 | Real estate funds |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 3 | Cash and accrued income |  |
Assets |  |
Total postretirement benefit plan assets | 0 | 0
Level 3 | Derivatives designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Level 3 | Derivatives designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Level 3 | Derivatives not designated as hedging instruments | Commodity Contracts |  |
Assets |  |
Derivatives, net | 0 | 0
Level 3 | Derivatives not designated as hedging instruments | Foreign Exchange Contracts |  |
Assets |  |
Derivatives, net | $ 0 | 0
Level 3 | Derivatives not designated as hedging instruments | Interest Rate Lock Contract |  |
Assets |  |
Derivatives, net |  | $ 0

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