XML 99 R70.htm IDEA: XBRL DOCUMENT v3.10.0.1
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, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 1 year 3 months 18 days 1 year 2 months 12 days 1 year 2 months 12 days
Expected volatility 35.20% 26.80% 30.50%
Risk-free interest rate 2.20% 1.00% 0.70%
Expected dividends 0.00% 0.00% 0.00%
Weighted average fair value at grant date (usd per share) $ 94.71 $ 31.36 $ 22.23