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

Stockholders' Equity (Deficit) - Schedule of Stock-based Compensation Expense (Detail)

v3.8.0.1
Stockholders' Equity (Deficit) - Schedule of Stock-based Compensation Expense (Detail) - USD ($)
$ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense $ 13,611 $ 1,588 $ 1,730 $ 127
Sales and Marketing [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense 276 51 71 80
Research and Development [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense 261 17 31 20
General and Administrative [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense 13,074 1,520 1,628 27
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense 629 78 151 54
Common Stock Awards [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense 250 1,442 1,442  
Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense 12,708 $ 68 $ 137 $ 73
Employee Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense $ 24