Summary of Stock Option Activity (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013
Shares Available for Grant
Balance at December 31, 2012	593,011
Options authorized	150,000
Options granted	(785,241)
Options cancelled	326,274
Balance at September 30, 2013	284,044
Shares Subject to Outstanding Options
Balance at December 31, 2012	3,451,178
Options granted	785,241
Options exercised	(129,787)
Options cancelled	(326,274)
Balance at September 30, 2013	3,780,358
Weighted-Average Exercise Price Per Share
Balance at December 31, 2012	$ 6.35
Options granted	$ 17.29
Options exercised	$ 22.67
Options cancelled	$ 7.81
Balance at September 30, 2013	$ 7.94