Share-Based Compensation - Additional Information (Detail)	9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Employee Stock Purchase Plan	Sep. 30, 2011 Employee Stock Purchase Plan	Sep. 30, 2012 Employee Stock Purchase Plan	Sep. 30, 2011 Employee Stock Purchase Plan	May 02, 2012 Stock Option Plan 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for option grants							3,000,000
Options granted	2,822,990	2,998,390
Issuance of shares under stock purchase plan			773,661	663,386	773,661	663,386