Annual report pursuant to Section 13 and 15(d)

Common Stock - Summary of Stock Options Outstanding Regarding Number of Common Shares Issuable upon Exercise of Outstanding Options (Detail)

v3.19.1
Common Stock - Summary of Stock Options Outstanding Regarding Number of Common Shares Issuable upon Exercise of Outstanding Options (Detail)
 12 Months Ended
Dec. 31, 2018
$ / shares
shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Number of Outstanding Options | shares 665,585
Exercise Price Range, Weighted Average Exercise Price $ 15.65
Exercise Price Range, Weighted Average Remaining Contractual Life 9 years 5 months 15 days
Range one [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 2.56
Exercise Price Range, Upper Range Limit $ 2.97
Exercise Price Range, Number of Outstanding Options | shares 386,650
Exercise Price Range, Weighted Average Exercise Price $ 2.56
Exercise Price Range, Weighted Average Remaining Contractual Life 9 years 8 months 19 days
Range two [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 2.98
Exercise Price Range, Upper Range Limit $ 16.13
Exercise Price Range, Number of Outstanding Options | shares 167,750
Exercise Price Range, Weighted Average Exercise Price $ 3.37
Exercise Price Range, Weighted Average Remaining Contractual Life 9 years 6 months 25 days
Range three [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 16.14
Exercise Price Range, Upper Range Limit $ 69.45
Exercise Price Range, Number of Outstanding Options | shares 104,910
Exercise Price Range, Weighted Average Exercise Price $ 28.90
Exercise Price Range, Weighted Average Remaining Contractual Life 8 years 6 months 29 days
Range four [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 69.46
Exercise Price Range, Upper Range Limit $ 157.30
Exercise Price Range, Number of Outstanding Options | shares 408
Exercise Price Range, Weighted Average Exercise Price $ 110.00
Exercise Price Range, Weighted Average Remaining Contractual Life 7 years 4 months 24 days
Range five [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 157.31
Exercise Price Range, Upper Range Limit $ 206.25
Exercise Price Range, Number of Outstanding Options | shares 1,782
Exercise Price Range, Weighted Average Exercise Price $ 204.60
Exercise Price Range, Weighted Average Remaining Contractual Life 6 years 4 months 17 days
Range six [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 206.26
Exercise Price Range, Upper Range Limit $ 1,228.15
Exercise Price Range, Number of Outstanding Options | shares 835
Exercise Price Range, Weighted Average Exercise Price $ 448.47
Exercise Price Range, Weighted Average Remaining Contractual Life 5 years 6 months 10 days
Range seven [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 1,228.16
Exercise Price Range, Upper Range Limit $ 1,305.70
Exercise Price Range, Number of Outstanding Options | shares 907
Exercise Price Range, Weighted Average Exercise Price $ 1,296.49
Exercise Price Range, Weighted Average Remaining Contractual Life 5 years 1 month 24 days
Range eight [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 1,305.71
Exercise Price Range, Upper Range Limit $ 1,405.80
Exercise Price Range, Number of Outstanding Options | shares 713
Exercise Price Range, Weighted Average Exercise Price $ 1,321.28
Exercise Price Range, Weighted Average Remaining Contractual Life 4 years 1 month 13 days
Range nine [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 1,405.81
Exercise Price Range, Upper Range Limit $ 1,659.35
Exercise Price Range, Number of Outstanding Options | shares 605
Exercise Price Range, Weighted Average Exercise Price $ 1,443.12
Exercise Price Range, Weighted Average Remaining Contractual Life 3 years 2 months 15 days
Range ten [Member]  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Exercise Price Range, Lower Range Limit $ 1,659.36
Exercise Price Range, Upper Range Limit $ 2,450.80
Exercise Price Range, Number of Outstanding Options | shares 1,025
Exercise Price Range, Weighted Average Exercise Price $ 2,007.37
Exercise Price Range, Weighted Average Remaining Contractual Life 1 year 7 months 24 days