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Fair value measurements (Tables)
 9 Months Ended
Sep. 30, 2017
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, 2017 and December 31, 2016:
 
Level 1
 
Level 2
 
Level 3
 
Balance as of September 30, 2017
Cash equivalents
$
6,326,982

 
$
—

 
$
—

 
$
6,326,982

Marketable securities:
 
 
 
 
 
 
 
U.S. government agency securities
—

 
12,481,959

 
—

 
12,481,959

Commercial paper
—

 
6,294,431

 
—

 
6,294,431

 
$
6,326,982

 
$
18,776,390

 
$
—

 
$
25,103,372



 
Level 1
 
Level 2
 
Level 3
 
Balance as of December 31, 2016
Cash equivalents
$
11,681,074

 
$
—

 
$
—

 
$
11,681,074

Marketable securities:
 
 
 
 
 
 
 
U.S. government agency securities
—

 
31,059,491

 
—

 
31,059,491

Commercial paper
—

 
6,081,202

 
—

 
6,081,202

Corporate debt securities
—

 
1,518,240

 
—

 
1,518,240

 
$
11,681,074

 
$
38,658,933

 
$
—

 
$
50,340,007