Activity Under Stock Plans (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shares Available For Grant
Beginning Balances	1,011,650	318,690	522,497
Additional shares authorized	1,123,131	912,544
Stock awards granted		(72,441)	(134,530)
Options granted	(444,607)	(324,585)	(145,375)
Options canceled	421,987	165,980	76,098
Options exercised	78,124	35,087	147,154
Stock awards canceled and forfeited	16,894	11,462
Ending Balances	2,129,055	1,011,650	318,690
Number of Shares Subject to Options Outstanding
Beginning Balances	1,086,299	962,781	1,040,658
Additional shares authorized	1,123,131	912,544
Stock awards granted		72,441	134,530
Options granted	444,607	324,585	145,375
Options canceled	(421,987)	(165,980)	(76,098)
Options exercised	(78,124)	(35,087)	(147,154)
Stock awards canceled and forfeited
Ending balances	1,030,795	1,086,299	962,781
Options vested and expected to vest at end of period	979,255
Weighted Average Exercise Price
Beginning Balances	$ 1.18	$ 1.07	$ 1.00
Options granted	$ 4.77	$ 1.46	$ 1.46
Options canceled	$ 1.26	$ 1.25	$ 1.07
Options exercised	$ 1.08	$ 0.96	$ 0.82
Ending Balances	$ 2.68	$ 1.18	$ 1.07
Options vested and expected to vest at end of period	$ 2.68