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Post-Retirement Obligation- Summary of Actuarial Assumptions (Detail)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of fair value of plan assets [abstract]      
Annual discount rate for present value of the actuarial obligation 9.48% 10.50% 13.20%
Annual expected return on plan assets 9.48% 10.50% 13.20%
Long-term annual inflation rate 4.00% 4.50% 5.50%
Estimated future annual salary increases 6.08% 6.59% 7.61%
General mortality table AT-2000 D10 AT-2000 AT-2000
Disability table Not adopted Álvaro Vindas Álvaro vindas
Disabled mortality table AT 49 AT 49 AT 49