Employee Benefits and Share-Based Compensation - Summary of Shares Reserved for Future Issuance Under Equity Incentive Plans (Details) shares in Thousands	Dec. 31, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved for future issuance	8,847
1997 Employee Stock Purchase Plan | ESPP shares available for future issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved for future issuance	1,913
2009 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved for future issuance	6,900
2009 Plan | Share options outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved for future issuance	3,748
2009 Plan | Non-vested restricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved for future issuance	755
2009 Plan | Shares authorized for future issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares reserved for future issuance	2,431