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Fair value measurements (Tables)
9 Months Ended
Sep. 30, 2016
Fair Value Disclosures [Abstract]  
Summary of Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis
The following tables summarize the cash equivalents and marketable securities measured at fair value on a recurring basis as of September 30, 2016 and December 31, 2015:
 
Level 1
 
Level 2
 
Level 3
 
Balance as of
September 30, 2016
Cash equivalents
$
20,697,042

 
$

 
$

 
$
20,697,042

Marketable securities:
 
 
 
 
 
 
 
Corporate debt securities

 
11,418,230

 

 
11,418,230

U.S. government agency securities

 
28,086,033

 

 
28,086,033

 
$
20,697,042

 
$
39,504,263

 
$

 
$
60,201,305



 
Level 1
 
Level 2
 
Level 3
 
Balance as of December 31, 2015
Cash equivalents
$
58,575,348

 
$
1,410,322

 
$

 
$
59,985,670

Marketable securities:
 
 
 
 
 
 
 
      Corporate debt securities

 
26,965,297

 

 
26,965,297

 
$
58,575,348

 
$
28,375,619

 
$

 
$
86,950,967