Summary of Stock Option Activity (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013
Share Available for Grant
Balance at December 31, 2012	593,011
Options authorized	150,000
Options granted	(560,854)
Options cancelled	151,913
Balance at June 30, 2013	334,070
Shares Subject to Outstanding Options
Balance at December 31, 2012	3,451,178
Options granted	560,854
Options exercised	(72,204)
Options cancelled	(151,913)
Balance at June 30, 2013	3,787,915
Weighted-Average Exercise Price Per Share
Balance at December 31, 2012	$ 6.35
Options granted	$ 13.98
Options exercised	$ 3.52
Options cancelled	$ 7.33
Balance at June 30, 2013	$ 7.50