Employee benefits - Projected benefit payments (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2020	$ 48,161
2021	45,152
2022	45,295
2023	45,498
2024	45,696
2025- 2029	228,701
OPEB Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
2020	6,515
2021	6,510
2022	6,661
2023	6,843
2024	7,057
2025- 2029	$ 38,483

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in fifth fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year.

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