Cash equivalents and marketable securities (Details)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 14,130,970
Unrealized Gains		38
Unrealized Losses		(1,285)
Fair Value	$ 0	$ 14,129,723
Number of debt securities in an unrealized loss position \| security		6
Aggregate fair value of debt securities in an unrealized loss position		$ 8,191,315
Number of debt securities in a significant unrealized loss position \| security		0
U.S. government agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 8,987,254
Unrealized Gains		38
Unrealized Losses		(1,033)
Fair Value		8,986,259
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		4,440,689
Unrealized Gains		0
Unrealized Losses		0
Fair Value		4,440,689
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		703,027
Unrealized Gains		0
Unrealized Losses		(252)
Fair Value		$ 702,775

Debt Securities, Available-for-sale, Significant Unrealized Loss Position, Number of Positions

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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