Pension and other postretirement benefits - expected benefit payments (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Pension
Schedule Of Pension Expected Future Benefit Payments [Line Items]
2019	$ 20,852
2020	21,023
2021	21,795
2022	22,658
2023	23,161
Years 2024 — 2028	124,927
Other Benefits
Schedule Of Pension Expected Future Benefit Payments [Line Items]
2019	3,972
2020	4,024
2021	3,893
2022	4,015
2023	3,795
Years 2024 — 2028	$ 15,241

Schedule of Pension Expected Future Benefit Payments [Line Items]

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- Definition

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

+ References

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=108410482&loc=d3e1928-114920

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- Definition

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

+ References

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- Definition

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.

+ References

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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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