General form of registration statement for all companies including face-amount certificate companies

Summary of Significant Accounting Policies - Consolidated Statement of Operations - Correction of Error (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Consolidated Statement of Operations - Correction of Error (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]        
Interest expense     $ (3,890)  
Other income (expense)     697  
Other income (expense), net $ (12,872) $ (1,483) (3,193) $ 85
Loss before provision for income taxes (46,806) (17,910) (26,973) (6,205)
Net loss (46,811) (17,915) (26,979) (6,210)
Net loss attributable to common stockholders $ (51,281) $ (20,298) $ (30,183) $ (9,540)
Basic and diluted net loss per share attributable to common stockholders $ (5.94) $ (10.37) $ (14.59) $ (6.73)
Weighted-average shares used to compute basic and diluted net loss per share 8,640,178 1,957,596 2,068,334 1,416,732
Originally Reported [Member]        
Error Corrections and Prior Period Adjustments Restatement [Line Items]        
Interest expense     $ (430)  
Other income (expense)     950  
Other income (expense), net     520  
Loss before provision for income taxes     (23,260)  
Net loss     (23,266)  
Net loss attributable to common stockholders     $ (26,470)  
Basic and diluted net loss per share attributable to common stockholders     $ (12.80)  
Weighted-average shares used to compute basic and diluted net loss per share     2,068,334  
Restatement Adjustment [Member]        
Error Corrections and Prior Period Adjustments Restatement [Line Items]        
Interest expense     $ (3,460)  
Other income (expense)     (253)  
Other income (expense), net     (3,713)  
Loss before provision for income taxes     (3,713)  
Net loss     (3,713)  
Net loss attributable to common stockholders     $ (3,713)  
Basic and diluted net loss per share attributable to common stockholders     $ (1.79)