Stock-Based Compensation - Schedule of Stock Options Activity (Detail) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
NUMBER OF SHARES
Beginning balance (in shares) | shares	6,457,343
Granted (in shares) | shares	793,236
Exercised (in shares) | shares	(41,857)
Canceled (in shares) | shares	(82,775)
Ending balance (in shares) | shares	7,125,947
Options exercisable (in shares) | shares	4,427,796
WEIGHTED AVERAGE EXERCISE PRICE
Beginning balance (in dollars per share) | $ / shares	$ 22.15
Granted (in dollars per share) | $ / shares	55.47
Exercised (in dollars per share) | $ / shares	19.61
Cancelled (in dollars per share) | $ / shares	46.18
Ending balance (in dollars per share) | $ / shares	25.57
Options exercisable (in dollars per share) | $ / shares	$ 14.58
WEIGHTED AVERAGE REMAINING CONTRACTUAL LIFE (YEARS)
Options outstanding, weighted average remaining contractual life (in years)	7 years 2 months 5 days
Options exercisable (in years)	6 years 1 month 4 days
AGGREGATE INTRINSIC VALUE
Options outstanding | $	$ 207,230
Options exercisable | $	$ 175,649