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Cash equivalents and marketable securities (Tables)
 3 Months Ended
Mar. 31, 2017
Cash and Cash Equivalents [Abstract]  
Schedule of Marketable Securities
Marketable securities at March 31, 2017 and December 31, 2016 consisted of the following:
 
Amortized Cost
 
Unrealized Gains
 
Unrealized Losses
 
Fair Value
As of March 31, 2017
 
 
 
 
 
 
 
Current (due within 1 year):
 
 
 
 
 
 
 
U.S. government agency securities
$
24,058,598

 
$
—

 
$
(12,308
)
 
$
24,046,290

Commercial paper
4,594,668

 
—

 
—

 
4,594,668

Corporate debt securities
3,102,173

 
—

 
(45
)
 
3,102,128

Total
$
31,755,439

 
$
—

 
$
(12,353
)
 
$
31,743,086

 
Amortized Cost
 
Unrealized Gains
 
Unrealized Losses
 
Fair Value
As of December 31, 2016
 
 
 
 
 
 
 
Current (due within 1 year):
 
 
 
 
 
 
 
U.S. government agency securities
$
31,060,710

 
$
2,912

 
$
(4,131
)
 
$
31,059,491

Commercial paper
6,081,202

 
—

 
—

 
6,081,202

Corporate debt securities
1,518,635

 
—

 
(395
)
 
1,518,240

Total
$
38,660,547

 
$
2,912

 
$
(4,526
)
 
$
38,658,933