Summary of Stock Options under Employee Equity Incentive Plan and Stock Option Plan for Non-Employee Directors (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares
Shares
Outstanding at beginning of period | shares	1,127,162
Granted | shares	800,490
Forfeited | shares	(40,352)
Expired | shares	(1,980)
Exercised | shares	(537,087)
Outstanding at end of period | shares	1,348,233
Exercisable at end of period | shares	196,522
Vested and expected to vest at end of period | shares	744,866
Weighted-Average Exercise Price
Outstanding at beginning of period | $ / shares	$ 63.99
Granted | $ / shares	197.56
Forfeited | $ / shares	196.86
Expired | $ / shares	241.79
Exercised | $ / shares	74.71
Outstanding at end of period | $ / shares	141.98
Exercisable at end of period | $ / shares	86.52
Vested and expected to vest at end of period | $ / shares	$ 97.34
Weighted-Average Remaining Contractual Term
Outstanding at end of period	6 years 5 months 9 days
Exercisable at end of period	4 years 1 month 21 days
Vested and expected to vest at end of period	4 years 4 months 21 days
Aggregate Intrinsic Value
Outstanding at end of period | $	$ 61,632
Exercisable at end of period | $	17,210
Vested and expected to vest at end of period | $	$ 59,410