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Cash equivalents and marketable securities (Details)	Mar. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 31,755,439	$ 38,660,547
Unrealized Gains	0	2,912
Unrealized Losses	(12,353)	(4,526)
Fair Value	$ 31,743,086	$ 38,658,933
Number of debt securities held | security	11	6
Aggregate fair value of debt securities in an unrealized loss position	$ 27,148,418	$ 16,519,620
US government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,058,598	31,060,710
Unrealized Gains	0	2,912
Unrealized Losses	(12,308)	(4,131)
Fair Value	24,046,290	31,059,491
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,594,668	6,081,202
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	4,594,668	6,081,202
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,102,173	1,518,635
Unrealized Gains	0	0
Unrealized Losses	(45)	(395)
Fair Value	$ 3,102,128	$ 1,518,240

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