Income taxes - Schedule of deferred tax assets and liabilities (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
U.S. and state net operating loss carryforwards	$ 11,118,289	$ 2,708,861
Accruals and other temporary differences	510,897	23,829
Amortization	33,824	36,742
Stock-based compensation	473,801	57,120
Tax credit carryforward	671,012	87,762
Total deferred tax assets	12,807,823	2,914,314
Less valuation allowance	(12,688,401)	(2,751,295)
Deferred tax assets	119,422	163,019
Deferred tax liabilities:
Stock-based compensation	(110,366)	(162,779)
Depreciation	(9,056)	(240)
Accruals and other temporary differences	0	0
Deferred tax liabilities	(119,422)	(163,019)
Net deferred tax assets	$ 0	$ 0