Shares Reserved for Issuance, Consisting of Both Shares Available For Awards and Shares Issuable Under Outstanding Stock Option (Detail)	Dec. 31, 2012
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Total shares reserved	8,997,060
1996 Directors Plan options
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Total shares reserved	40,784
1997 Stock Option Plan
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Total shares reserved	54,522
2000 Stock Option Plan
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Total shares reserved	232,096
2005 Stock Option Plan
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Total shares reserved	2,384,111
2008 Stock Option Plan
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Total shares reserved	3,285,547
2011 Stock Option Plan
Share Based Compensation Arrangements By Share Based Payment Award Options [Line Items]
Total shares reserved	3,000,000