Significant Accounting Policies - Summary of Assumptions for Options Granted (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Volatility factor	19.20%	23.60%	30.90%
Dividend yield	1.10%	0.90%	0.90%
Expected term (in years)	5 years 9 months 11 days	5 years 7 months 28 days	5 years 7 months 24 days
Risk-free rate	1.30%	1.60%	1.90%