Assumptions Used in Determining Fair Value of Options Granted (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected term of options in years	6 years 3 months 18 days	6 years 3 months 18 days	6 years 3 months 18 days
Expected volatility	38.50%
Expected volatility, minimum		39.00%	41.50%
Expected volatility, maximum		40.20%	42.50%
Risk-free interest rate, minimum	1.40%	1.50%	2.10%
Risk-free interest rate, maximum	1.60%	2.00%	2.30%
Expected dividend yield	0.00%	0.00%	0.00%