Note J - Common Stock and Warrants
 12 Months Ended
Dec. 31, 2016
Notes to Financial Statements  
Stockholders' Equity Note Disclosure [Text Block]
J.
Common Stock and Warrants
 
Authorized, Issued, and Outstanding Common Shares
 
In
April
2015,
the Company amended its Certificate of
Incorporation to increase the number of its authorized shares of common stock to
250,000,000
shares. Of the authorized shares,
14,646,982
and 
14,490,954
shares of common stock were issued and outstanding at
December
31,
2016
and
2015,
respectively.
 
At
Dec
ember
31,
2016
and
2015,
the Company had reserved authorized shares of common stock for future issuance as follows:
 
   
December 31,
  
   
2016
    
2015
  
Conversion of Deerfield Convertible Notes
    
1,751,296
      
1,991,219
  
Conversion of 2021 Notes    
 5,040,914
      
 —
  
Outstanding awards under equity incentive plans
    
1,990,260
      
1,397,511
  
Outstanding common stock warrants
    
2,087,477
      
2,325,383
  
Possible future issuances under equity incentive plans
    
1,244,671
      
1,410,848
  
Total
common shares reserved for future issuance
    
12,114,618
      
7,124,961
  
 
Common Stock Activity
 
The following table summarizes common stock activity for the year ended
December
31,
2016,
2015
and
2014:
 
   
Shares of
  
   
Common Stock
  
Balance at January 1, 2014    
2,381,041
  
Balance at December 31, 2014    
2,381,041
  
Issuance of common stock in connection with the IPO    
5,854,545
  
Conversion of preferred stock to common stock in connection with the IPO    
5,980,564
  
Common stock warrants exercised    
270,038
  
Common stock options exercised    
4,766
  
Balance at December 31, 2015
    
14,490,954
  
Common stock warrants exercised    
141,095
  
Common stock options exercised    
14,933
  
Balance at December 31, 2016    
14,646,982
  
 
 
The Company calculates the fair value of
common stock warrants using a Monte Carlo simulation. There were warrants exercised for an aggregate of 
141,095
and 
270,038
 shares of common stock during the years ended
December
31,
2016
and
2015,
respectively.
No
warrants were exercised during the year ended
December
31,
2014.
 From
2008
through
2012,
the Company issued warrants to purchase
595,920
shares of common stock in its private placement offerings of Series A redeemable convertible preferred stock, Series B redeemable convertible preferred stock and Series C redeemable convertible preferred stock (the “Underwriter Warrants”) and for leasing laboratory space. The Company accounted for the Underwriter Warrants as a derivative liability, which is adjusted to fair value at each reporting period, with the change in fair value recorded within other expenses in the statements of operations.