Accrued expenses and other current liabilities - Schedule of restructuring and related costs (Details)	12 Months Ended
Dec. 31, 2018 USD ($)
Restructuring Reserve [Roll Forward]
Accrued restructuring balance as of December 31, 2017	$ 0
Restructuring charges	1,366,000
Payments	(1,297,207)
Accrued restructuring balance as of December 31, 2018	68,593
Employee severance
Restructuring Reserve [Roll Forward]
Restructuring charges	1,136,388
Retention benefits
Restructuring Reserve [Roll Forward]
Restructuring charges	214,417
Other restructuring
Restructuring Reserve [Roll Forward]
Restructuring charges	$ 14,995

Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

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-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
-Paragraph 17
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-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3367-108585

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

+ References

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Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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