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Note Employee benefits (Accumulated benefit obligation in excess of plan assets) (Detail) - USD ($)
$ in Thousands
Dec. 31, 2015
Dec. 31, 2014
Pension Plan    
Defined Benefit Plan Disclosure [Line Items]    
Projected benefit obligation $ 736,140 $ 777,815
Accumulated benefit obligation 736,140 777,815
Fair value of plan assets 612,283 662,765
Benefit Restoration Plans    
Defined Benefit Plan Disclosure [Line Items]    
Projected benefit obligation 40,773 42,664
Accumulated benefit obligation 40,773 42,664
Fair value of plan assets $ 32,131 $ 34,475