Cash equivalents and marketable securities (Details)	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Marketable securities:
Amortized Cost	$ 38,660,547	$ 26,989,951
Unrealized Gains	2,912	1,878
Unrealized Losses	(4,526)	(26,532)
Fair Value	$ 38,658,933	$ 26,965,297
Number of debt securities held \| security	6	11
Aggregate fair value of debt securities in an unrealized loss position	$ 16,519,620	$ 24,967,915
Current Assets \| Corporate debt securities
Marketable securities:
Amortized Cost	1,518,635	24,666,607
Unrealized Gains	0	1,878
Unrealized Losses	(395)	(16,137)
Fair Value	1,518,240	24,652,348
Current Assets \| Commercial paper
Marketable securities:
Amortized Cost	6,081,202
Unrealized Gains	0
Unrealized Losses	0
Fair Value	6,081,202
Current Assets \| U.S. government agency securities
Marketable securities:
Amortized Cost	31,060,710
Unrealized Gains	2,912
Unrealized Losses	(4,131)
Fair Value	$ 31,059,491
Noncurrent Assets \| Corporate debt securities
Marketable securities:
Amortized Cost		2,323,344
Unrealized Losses		(10,395)
Fair Value		$ 2,312,949

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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