Cash equivalents and marketable securities (Details)	Sep. 30, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 39,489,591	$ 26,989,951
Unrealized Gains	18,271	1,878
Unrealized Losses	(3,599)	(26,532)
Fair Value	39,504,263	26,965,297
Marketable securities, current	39,504,263	24,652,348
Marketable securities, noncurrent	$ 0	$ 2,312,949
Number of debt securities held \| security	4	11
Aggregate fair value of debt securities in an unrealized loss position	$ 10,604,705	$ 24,967,915
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,418,571
Unrealized Gains	334
Unrealized Losses	(675)
Fair Value	11,418,230
Corporate debt securities \| Current Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		24,666,607
Unrealized Gains		1,878
Unrealized Losses		(16,137)
Fair Value		24,652,348
Corporate debt securities \| Noncurrent Assets
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,323,344
Unrealized Gains		0
Unrealized Losses		(10,395)
Fair Value		$ 2,312,949
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,071,020
Unrealized Gains	17,937
Unrealized Losses	(2,924)
Fair Value	$ 28,086,033

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

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