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Non-Current Provisions - Schedule of Retirement Commitments (Detail)
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of sensitivity analysis for actuarial assumptions [abstract]      
% social security contributions 50.00% 50.00% 50.00%
Salary increases 2.00% 2.00% 2.00%
Discount rate 1.30% 1.31% 2.08%