Stock Option Activity Under Stock Option Plan (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Number of Shares
Beginning Balance			7,147,303
Granted	1,315,500	361,900	1,426,400	425,400
Exercised			(455,168)
Cancelled			(1,580,116)
Ending Balance	6,538,419		6,538,419		7,147,303
Vested and unvested expected to vest at end of period	6,481,884		6,481,884
Options exercisable, at end of period	3,406,985		3,406,985		3,683,786
Options available for future grant	1,430,403		1,430,403
Weighted Average Exercise Price
Beginning Balance			$ 4.11
Granted			$ 2.49
Exercised			$ 1.87
Cancelled			$ 4.73
Ending Balance	$ 3.76		$ 3.76		$ 4.11
Vested and unvested expected to vest at end of period	$ 3.85		$ 3.85
Options exercisable, at end of period	$ 3.85		$ 3.85		$ 3.56
Weighted Average Contractual Term (Years)
Outstanding, at end of period			7 years 1 month 10 days
Vested and unvested expected to vest at end of period			5 years 11 days
Options exercisable, at end of period			5 years 11 days		5 years 3 months 11 days
Aggregate Intrinsic Value
Outstanding, at end of period	$ 956		$ 956
Vested and unvested expected to vest at end of period	948		948
Options exercisable, at end of period	$ 956		$ 956		$ 3,972