Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shares Available For Grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available, beginning balances	2,861	4,148	2,654
Options granted, increase in authorized shares	300	2,388	3,911
Options granted, shares available	(3,399)	(4,925)	(4,841)
Options canceled, number of shares	1,416	1,250	2,424
Shares available, ending balances	1,178	2,861	4,148
Shares Outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, beginning balances	9,744	6,928	4,841
Options granted, number of shares	3,399	4,925	4,841
Options canceled, number of shares	(1,416)	(1,250)	(2,424)
Options exercised, number of shares	(806)	(859)	(330)
Number of shares, ending balances	10,921	9,744	6,928
Weighted average exercise price, beginning balances	$ 2.80	$ 2.02	$ 3.49
Options vested and expected to vest, number of shares	9,429
Options granted, weighted average exercise price	$ 3.84	$ 3.66	$ 1.30
Options exercisable, number of shares	4,705
Options canceled, weighted average exercise price	$ 3.89	$ 2.50	$ 3.66
Options exercised, weighted average exercise price	$ 1.68	$ 1.90	$ 0.87
Weighted average exercise price, ending balances	$ 3.07	$ 2.80	$ 2.02
Options vested and expected to vest, weighted average exercise price, ending balances	$ 3.03
Options exercisable, weighted average exercise price, ending balances	$ 2.92
Weighted average contractual term, options outstanding	4 years 2 months 1 day
Weighted average contractual term, options vested and expected	4 years 11 days
Weighted average contractual term, Options exercisable	3 years 3 months 29 days
Aggregate intrinsic value, options outstanding	$ 3,684
Aggregate intrinsic value, Options vested and expected to vest	3,523
Aggregate intrinsic value, options exercisable	$ 2,517