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Stockholders' Equity - Additional Information (Detail) - USD ($)
 1 Months Ended 2 Months Ended 6 Months Ended 12 Months Ended
Feb. 13, 2017
Jul. 13, 2016
Jan. 12, 2016
Dec. 04, 2015
Apr. 10, 2015
Mar. 18, 2015
Nov. 18, 2014
May 24, 2013
Apr. 10, 2015
Feb. 28, 2017
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Feb. 06, 2017
Jul. 29, 2016
May 10, 2016
May 08, 2013
Class of Stock [Line Items]                                      
Preferred stock, shares authorized                     5,000,000   5,000,000 5,000,000          
Preferred stock, par value (usd per share)                     $ 0.0001   $ 0.0001 $ 0.0001          
Common stock, shares authorized                     350,000,000   350,000,000 275,000,000          
Common stock, par value (usd per share)                     $ 0.0001   $ 0.0001 $ 0.0001          
Proceeds from issuance of shares                     $ 5,000 $ 78,000 $ 95,000 $ 309,000 $ 263,000        
Issuance of common stock, shares     988,636             3,541,077                  
Net proceeds from issuance of common stock                     $ 15,524,000 $ 20,189,000 $ 33,534,000 $ 47,416,000 10,704,000        
Number of shares availabe from warrants                                     9,109
Exercise price   $ 13.00 $ 28.40               $ 79.40   $ 79.40 $ 79.40     $ 8.60 $ 30.20 $ 49.4
Proceeds from issuance of shares, net underwriting discounts, commissions and offering expenses     $ 20,200,000                                
Price per unit     $ 22.00                                
Issuance of common stock, value     $ 21,800,000             $ 3,950,000     $ 33,534,000 $ 47,416,000 $ 10,705,000        
Number of securities called by each warrant     0.60                                
Exercise period of warrants   5 years                                  
Period from issuance which warrants is exercisable   6 months 1 day                                  
Proceeds from issuance of warrants   $ 11,700,000                                  
Common Stock                                      
Class of Stock [Line Items]                                      
Issuance of common stock, shares   1,400,000                     2,872,803 1,607,934 331,650        
Price per unit   $ 9.00                                  
Issuance of common stock, value                         $ 0 $ 3,000 $ 1,000        
New warrants issued during period (in shares)   700,000                                  
Lincoln Park Capital, LLC Purchase Agreement                                      
Class of Stock [Line Items]                                      
Proceeds from issuance of shares             $ 4,900,000               $ 8,500,000        
Purchase agreement term             36 months                        
Stock issued during period related to purchase of assets             125,000                        
Share price             $ 40.00                        
Issuance of common stock, shares                         150,000 135,000 230,000        
Net proceeds from issuance of common stock                         $ 800,000 $ 4,400,000          
Remaining authorized repurchase amount                     $ 2,000,000         $ 2,100,000      
Lincoln Park Capital, LLC Purchase Agreement | Minimum                                      
Class of Stock [Line Items]                                      
Shares authorized under purchase agreement, shares                               55,000,000      
Authorized amount in stock repurchase program                               55,000,000      
Lincoln Park Capital, LLC Purchase Agreement | Maximum                                      
Class of Stock [Line Items]                                      
Shares authorized under purchase agreement, shares                               15,600,000      
Authorized amount in stock repurchase program                               $ 15,600,000      
Lincoln Park Capital, LLC Purchase Agreement | Common Stock                                      
Class of Stock [Line Items]                                      
Proceeds from issuance of shares             $ 50,000,000                        
Issuance of common stock, shares             31,561                        
MLV & Co. LLC and Maxim Group LLC                                      
Class of Stock [Line Items]                                      
Proceeds from issuance of shares                         $ 900,000 $ 2,300,000 $ 2,300,000        
Issuance of common stock, shares                         334,000 72,000 70,000        
Percent of gross proceeds               3.00%                      
At Market Issuance Sales Agreements, Maximum Gross Proceeds       $ 20,000,000       $ 20,000,000                      
Remaining authorized repurchase amount       $ 19,100,000                              
Underwritten Public Offering                                      
Class of Stock [Line Items]                                      
Common stock, shares authorized           182,692                          
Proceeds from issuance of shares           $ 38,000,000                          
Share price           $ 31.20                          
Issuance of common stock, shares           1,217,948                          
Number of shares availabe from warrants           0.50                          
Exercise price           $ 41.60                          
Shares issued, overallotment option           91,346                          
Proceeds from issuance of shares, net underwriting discounts, commissions and offering expenses         $ 5,400,000       $ 40,800,000                    
Underwritten Public Offering | Common Stock                                      
Class of Stock [Line Items]                                      
Issuance of common stock, shares 17,000,000                                    
Exercise price $ 1.10                                    
Proceeds from issuance of shares, net underwriting discounts, commissions and offering expenses $ 15,500,000                                    
Price per unit $ 1.00   $ 1.00                                
New warrants issued during period (in shares) 17,000,000                                    
Class Of Warrant Or Right, Issued, Fair Value $ 10,400,000                                    
Over-Allotment Option                                      
Class of Stock [Line Items]                                      
Number of shares availabe from warrants     88,977                                
Stock available for issuance under warrants     148,295