Stock-Based Compensation - Schedule of Stock Options Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
NUMBER OF SHARES
Beginning balance (in shares) | shares	6,457,343
Granted (in shares) | shares	1,207,984
Exercised (in shares) | shares	(600,690)
Canceled (in shares) | shares	(112,998)
Ending balance (in shares) | shares	6,951,639
Options exercisable (in shares) | shares	4,440,403
WEIGHTED AVERAGE EXERCISE PRICE
Beginning balance (in dollars per share) | $ / shares	$ 22.15
Granted (in dollars per share) | $ / shares	56.81
Exercised (in dollars per share) | $ / shares	8.74
Cancelled (in dollars per share) | $ / shares	46.01
Ending balance (in dollars per share) | $ / shares	28.92
Options exercisable (in dollars per share) | $ / shares	$ 18.39
WEIGHTED AVERAGE REMAINING CONTRACTUAL LIFE (YEARS)
Options outstanding, weighted average remaining contractual life	6 years 11 months 15 days
Options exercisable	5 years 11 months 5 days
AGGREGATE INTRINSIC VALUE
Options outstanding | $	$ 227,793
Options exercisable | $	$ 191,690