Note Employee benefits (Accumulated benefit obligation in excess of plan assets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 754,558	$ 816,988
Accumulated benefit obligation	754,558	816,988
Fair value of plan assets	685,823	767,539
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	153,415	170,720
Accumulated benefit obligation	153,415	170,720
Fair value of plan assets	$ 0	$ 0

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Amount of accumulated benefit obligation for defined benefit plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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Amount of plan asset for defined benefit plan with accumulated benefit obligation in excess of plan assets.

+ References

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Amount of projected benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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