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

Summary of Significant Accounting Policies - Consolidated Balance Sheet - Correction of Error (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Consolidated Balance Sheet - Correction of Error (Detail) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]        
Total current assets $ 78,509 $ 21,367 $ 27,274  
Total assets 79,682 22,348 28,266  
Convertible note payable, net of discount   13,388    
Total current liability 31,836 44,501 27,670  
Total liabilities 31,850 44,523 27,698  
Additional paid-incapital 144,396 (293) (4,527)  
Accumulated deficit (96,517) (45,236) (15,053)  
Total stockholders' equity (deficit) 47,832 (45,525) (19,578) $ (9,375)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit) $ 79,682 22,348 $ 28,266  
Originally Reported [Member]        
Error Corrections and Prior Period Adjustments Restatement [Line Items]        
Deferred offering costs   8,317    
Total current assets   29,684    
Total assets   30,665    
Convertible note payable, net of discount   19,804    
Total current liability   50,917    
Total liabilities   50,939    
Additional paid-incapital   (2,105)    
Accumulated deficit   (41,523)    
Total stockholders' equity (deficit)   (43,624)    
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)   30,665    
Restatement Adjustment [Member]        
Error Corrections and Prior Period Adjustments Restatement [Line Items]        
Deferred offering costs   (8,317)    
Total current assets   (8,317)    
Total assets   (8,317)    
Convertible note payable, net of discount   (6,416)    
Total current liability   (6,416)    
Total liabilities   (6,416)    
Additional paid-incapital   1,812    
Accumulated deficit   (3,713)    
Total stockholders' equity (deficit)   (1,901)    
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)   $ (8,317)