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Stock-Based Compensation - Additional Information (Detail)
1 Months Ended 12 Months Ended
Sep. 03, 2013
Sep. 30, 2006
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Dec. 31, 2014
shares
Dec. 31, 2013
shares
May 24, 2018
shares
May 25, 2017
shares
Jun. 08, 2016
shares
May 07, 2015
shares
Oct. 29, 2013
shares
Jun. 19, 2012
shares
Dec. 31, 2011
shares
Dec. 31, 2009
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Common stock, capital shares reserved for future issuance               40,940,000 25,940,000            
Stock-based compensation expense | $     $ 9,039,000 $ 7,078,000 $ 5,033,000                    
Expected dividend yield     0.00% 0.00% 0.00%                    
Aggregate intrinsic value of stock options outstanding | $     $ 9,200,000                        
Aggregate intrinsic value of stock options exercisable | $     2,300,000                        
Aggregate intrinsic value of stock options vested or expected to vest | $     8,700,000                        
Intrinsic value of options exercised | $     9,313,000 $ 2,179,000 $ 519,000                    
Proceeds from options exercised | $     $ 7,128,000 $ 438,000 $ 166,000                    
Options granted     8,705,617 4,746,250 5,368,755                    
Weighted-average grant date fair value of options granted | $ / shares     $ 1.59 $ 0.82 $ 1.30                    
Unrecognized employee stock-based compensation expense | $     $ 14,429,000                        
Expected weighted-average period for compensation expense recognition     2 years 8 months 12 days                        
Incentive Compensation Plan 2006 [Member]                              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Award limitations for options or stock appreciation rights per-person   80,000                          
Stock option, number of shares authorized for issuance                           3,378,189 1,110,053
Options vesting period     4 years                        
Options expiration period     10 years                        
Stock Appreciation Rights (SARs) [Member] | Incentive Compensation Plan 2007 [Member]                              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Award limitations for options or stock appreciation rights per-person           1,000,000 200,000                
Other Stock Based Awards [Member] | Incentive Compensation Plan 2007 [Member]                              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Award limitations for options or stock appreciation rights per-person           500,000 100,000                
June 19, 2012 Amendment [Member]                              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Common stock, capital shares reserved for future issuance                         1,000,000    
October 29, 2013 Amendment [Member]                              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Common stock, capital shares reserved for future issuance                       4,940,000      
May 7, 2015 Amendment [Member]                              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Common stock, capital shares reserved for future issuance                     11,940,000        
June 8, 2016 Amendment [Member]                              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Common stock, capital shares reserved for future issuance                   18,940,000          
Merger Agreement [Member]                              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                              
Option exchange ratio 1.1533