Stockholders' Equity - Weighted Average Assumptions Used for the Fair Value of the Option Component of the Purchase Plan Shares Estimated at Grant Date Using Black-Scholes Option Pricing Model (Detail) - Employee Stock Purchase Plan - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	1 year 4 months 24 days	1 year 3 months 18 days	1 year 2 months 12 days
Expected volatility	50.00%	35.20%	26.80%
Risk-free interest rate	2.20%	2.20%	1.00%
Expected dividends	0.00%	0.00%	0.00%
Weighted average fair value at grant date (usd per share)	$ 86.02	$ 94.71	$ 31.36