Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Schedule of Weighted Average Fair Value of Options Granted (Detail)

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Summary of Significant Accounting Policies - Schedule of Weighted Average Fair Value of Options Granted (Detail) - Performance Based Nonvested [Member] - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Schedule Of Weighted Average Assumptions For Fair Values Of Stock Options [Line Items]      
Expected life (years) 3 years 3 years 3 years
Risk free interest rate 2.62% 1.79% 1.53%
Expected volatility 21.36% 19.92% 19.37%
Fair value $ 93.26 $ 82.06 $ 80.24