Note Employee benefits (Changes in level 3 assets measured at fair value) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation
Fair value of plan assets at beginning of year	$ 767,539
Fair value of plan assets at end of year	685,823	$ 767,539
Level 3
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation
Fair value of plan assets at beginning of year	4,758	3,555
Actual return on plan assets	0	0
Purchases, sales, issuance, settlements, paydowns and maturities (net)	334	1,203
Fair value of plan assets at end of year	$ 5,092	$ 4,758

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

+ References

+ Details

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- Details

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