Stockholders' Equity - Schedule of Reserve for Authorized but Unissued Shares of Common Stock (Detail)	Dec. 31, 2012	Sep. 30, 2007
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased number of common shares in reserve	20,302,393
Common Stock Options and Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased number of common shares in reserve	8,029,465
Employee Stock Purchase Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased number of common shares in reserve	3,129,238
3.00% Convertible Subordinated Notes [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased number of common shares in reserve	4,711,283	4,711,283
4.75% Convertible Subordinated Notes [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased number of common shares in reserve	4,432,638