XML 65 R53.htm IDEA: XBRL DOCUMENT v3.8.0.1
Share-Based Compensation - Summary of Weighted Average Assumptions Used for Options Granted (Detail) - Stock Option Plan
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected life (in years) 6 years 6 years 6 years
Expected volatility 28.10% 29.30% 28.30%
Risk-free interest rate 2.00% 1.80% 1.70%
Expected forfeiture rate 0.00% 0.00% 1.70%