XML 48 R24.htm IDEA: XBRL DOCUMENT v3.20.1
Note 7 - Stock-based Compensation (Tables)
 12 Months Ended
Dec. 31, 2019
Notes Tables  
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]
    Year Ended December 31,
    2019   2018   2017
Research and development   $
13,977
     $
6,867
     $
9,602
  
General and administrative    
3,742
      
2,529
      
3,019
  
Total stock-based compensation expense   $
17,719
     $
9,396
     $
12,621
  
Share-based Payment Arrangement, Activity [Table Text Block]
    Awards
Available		   Options
Outstanding		   Weighted
Average
Exercise
Price
Balance at December 31, 2016    
2,273
      
12,095
     $
6.55
  
Plan amendment    
1,000
      
-
      
-
  
Restricted stock awards granted    
(22
 )    
-
      
-
  
Restricted stock awards cancelled    
12
      
-
      
-
  
Stock option awards granted    
(3,915
 )    
3,915
      
5.33
  
Stock option awards exercised    
-
      
(438
 )    
3.50
  
Stock option awards cancelled    
1,120
      
(1,120
 )    
9.72
  
Balance at December 31, 2017    
468
      
14,452
      
6.06
  
Plan amendment    
4,400
      
-
      
-
  
Restricted stock awards granted    
(13
 )    
-
      
-
  
Stock option awards granted    
(4,272
 )    
4,272
      
7.15
  
Stock option awards exercised    
-
      
(1,011
 )    
2.92
  
Stock option awards cancelled    
222
      
(222
 )    
7.44
  
Balance at December 31, 2018    
805
      
17,491
      
6.49
  
Plan amendment    
4,000
      
-
      
-
  
Restricted stock awards granted    
(27
 )    
-
      
-
  
Stock option awards granted    
(4,511
 )    
4,511
      
3.91
  
Stock option awards exercised    
-
      
(251
 )    
3.75
  
Stock option awards cancelled    
701
      
(701
 )    
6.82
  
Balance at December 31, 2019    
968
      
21,050
     $
5.96
  
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
    2019   2018   2017
Expected Life    
5.5
      
5.5
      
5.5
  
Expected Volatility    
81
 %    
82
 %    
82
 %
Expected Dividend Yield    
0.0
 %    
0.0
 %    
0.0
 %
Risk-Free Interest Rate    
1.8
 %    
2.7
 %    
2.0
 %
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding and Exercisable [Table Text Block]
   
Outstanding
  
Exercisable
Range
  
Number
  
Weighted
Average
Remaining
Life
  
Weighted
Average
Exercise
Price
  
Number
  
Weighted
Average
Exercise
Price
$
0
to
3
  
1,929
    
5.5
     $
2.02
      
1,159
     $
1.64
  
 
3
to
6
  
11,724
    
7.2
      
4.17
      
5,085
      
4.55
  
 
6
to
9
  
4,941
    
7.7
      
7.14
      
1,830
      
6.98
  
 
9
to
12
  
3,086
    
5.3
      
10.78
      
2,013
      
10.91
  
 
12
to
15
  
604
    
5.1
      
12.29
      
509
      
12.31
  
 
15
to
18
  
95
    
5.5
      
15.39
      
95
      
15.39
  
$
0
to
18
  
22,379
    
6.9
     $
5.82
      
10,691
     $
6.31
  
Share-based Payment Arrangement, Option, Activity [Table Text Block]
    Non-Vested
Stock Option
Awards		   Weighted Average
Grant-Date Fair
Value
Balance December 31, 2018    
9,295
     $
4.78
  
Stock option awards granted    
5,891
      
2.58
  
Stock option awards vested    
(2,794
 )    
4.48
  
Stock option awards forfeited    
(704
 )    
4.38
  
Balance December 31, 2019    
11,688
     $
3.77