Note Employee benefits (Contributions to the benefit plans) (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions to the benefit plans during the next year	$ 0
Benefit Restoration Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected employer contributions to the benefit plans during the next year	$ 236

Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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