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Cash equivalents and marketable securities (Tables)
 9 Months Ended
Sep. 30, 2016
Cash and Cash Equivalents [Abstract]  
Schedule of Marketable Securities
Marketable securities at September 30, 2016 and December 31, 2015 consisted of the following:
 
Amortized Cost
 
Unrealized Gains
 
Unrealized Losses
 
Fair Value
As of September 30, 2016
 
 
 
 
 
 
 
Current (due within 1 year):
 
 
 
 
 
 
 
Corporate debt securities
$
11,418,571

 
$
334

 
$
(675
)
 
$
11,418,230

U.S. government agency securities
28,071,020

 
17,937

 
(2,924
)
 
28,086,033

Total
$
39,489,591

 
$
18,271

 
$
(3,599
)
 
$
39,504,263

 
Amortized Cost
 
Unrealized Gains
 
Unrealized Losses
 
Fair Value
As of December 31, 2015
 
 
 
 
 
 
 
Current (due within 1 year):
 
 
 
 
 
 
 
    Corporate debt securities
$
24,666,607

 
$
1,878

 
$
(16,137
)
 
$
24,652,348

Noncurrent (due after 1 year through 5 years):
 
 
 
 
 
 
 
    Corporate debt securities
2,323,344

 
—

 
(10,395
)
 
2,312,949

Total
$
26,989,951

 
$
1,878

 
$
(26,532
)
 
$
26,965,297