XML 137 R115.htm IDEA: XBRL DOCUMENT v3.8.0.1
Stock-Based Compensation - Assumptions Used Under Black-Scholes Option Pricing Model (Detail)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free rate, Minimum 1.90% 1.10% 1.50%
Risk-free rate, Maximum 2.10% 1.40% 1.70%
Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility 27.38% 27.58% 27.95%
Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility 27.47% 27.70% 28.00%
TSR-based Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility 26.00% 27.60%  
Dividend yield 0.00% 0.00%  
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term 1 year 6 months 25 days 3 years  
Fair Value Assumptions, Risk Free Interest Rate 1.83% 0.87%  
Equity Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend yield 0.00% 0.00% 0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term 6 years 6 years 6 years