Note Employee benefits (Accumulated other comprehensive loss expected to be recognized as components of net periodic benefit cost) (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($)
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 20,215
Benefit Restoration Plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 1,645

Amount included in accumulated other comprehensive income (AOCI) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position, including gain (loss), prior service cost (credit), and transition asset (obligation).

No definition available.

Name:	us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration