Note M - Income Taxes (Tables)
 12 Months Ended
Dec. 31, 2016
Notes Tables  
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]
   
Year ended December 31,
  
   
2016
    
2015
    
2014
  
Federal statutory rate
    
34.00
%
    
34.00
%
    
34.00
%
Effect of:
                        
Change in valuation allowance
    
(69.31
)
    
(19.25
)
    
(32.88
)
Return to provision and deferred true-up    
(23.83
 )    
—
      
0.36
  
Change in rate    
(14.63
 )    
—
      
—
  
State tax benefit (net of federal)
    
15.64
      
4.06
      
5.96
  
Warrant liability
    
68.44
 
    
(15.28
)
    
(9.39
 ) 
State research and development credit
    
0.09
      
0.03
      
0.09
  
Federal research and development credit
    
5.65
      
0.84
      
3.29
  
Amortization    
(3.15
 )    
—
      
—
  
Conversion feature and put option on 2013 convertible
notes
    
—
 
    
(1.68
)
    
(1.26
)
Interest expense
    
—
      
—
      
0.21
 
Stock-based compensation
    
(12.71
)
    
(1.28
 )     
—
  
Other
    
(0.10
)
    
(1.42
 )     
(0.29
)
Federal income tax provision effective rate
    
0.09
%
    
0.02
%
    
0.09
%
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]
   
December 31,
    
December 31,
    
December 31,
  
   
2016
    
2015
    
2014
  
Deferred tax assets relating to:
                        
Net operating loss carryforwards
   $
44,984
     $
26,617
     $
16,390
  
Research and development tax carryforward
    
3,166
      
2,254
      
1,793
  
Compensation
    
715
      
232
      
83
  
Total gross deferred tax assets
    
48,865
      
29,103
      
18,266
  
Deferred tax liabilities relating to:
                        
Property and equipment
    
89
      
80
      
170
  
Total gross
deferred tax liabilities
    
89
      
80
      
170
  
Deferred tax assets less liabilities
    
48,776
      
29,023
      
18,096
  
Valuation allowance
    
(48,776
)
    
(29,023
)
    
(18,096
)
Net deferred tax asset (liability)
   $
—
     $
—
     $
—
  
Summary of Operating Loss Carryforwards [Table Text Block]
   
Net Operating
    
Research
    
 
 
 
Year Incurred
  
Loss Carryforwards
    
Activities Credit
    
Expiration
  
2007
   $
454
     $
30
      
2027
  
2008
    
1,178
      
65
      
2028
  
2009
    
3,060
      
176
      
2029
  
2010
    
3,423
      
149
      
2030
  
2011
    
9,929
      
176
      
2031
  
2012
    
—
      
170
      
2032
  
2013
    
4,353
      
133
      
2033
  
2014
    
15,819
      
894
      
2034
  
2015
    
24,189
      
461
      
2035
  
2016    
 40,959
      
 912
      
 2036
  
    $
103,364
     $
3,166