Stock Benefit Plans and Stock-Based Compensation - Summary Common Stock Reserved for Future Issuance (Detail) shares in Thousands	Dec. 31, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	39,438
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	4,682
Unvested restricted share awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	3,270
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	226
Series A Convertible Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	2,022
Convertible notes
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	988
Warrants Outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	22,302
Distributor And Development Services Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	4,000
Merger Contingently Issuable
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	887
Authorized for Future Grant Under the Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance	1,061