Income taxes (Details) - USD ($)	6 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2016	Dec. 31, 2015
Income Tax Expense (Benefit), Continuing Operations, by Jurisdiction [Abstract]
Current Federal Tax Expense (Benefit)		$ 180,000
Current Income Tax Expense (Benefit), Total		180,000
Deferred Federal Income Tax Expense (Benefit)		(111,000)
Deferred State and Local Income Tax Expense (Benefit)		(17,000)
Deferred Income Tax Expense (Benefit), Total		(128,000)
Income Tax Expense (Benefit), Total		52,000	$ 0
Accrued income tax provision		200,000
Deferred tax assets:
Deferred Tax Assets, Operating Loss Carryforwards		8,927,000	12,521,000
Tax credit carryforwards		4,284,000	1,969,000
Deferred rent		1,964,000	516,000
Deferred revenue		16,333,000
Non‑deductible expenses		714,000	577,000
Intangibles		998,000	376,000
Stock Compensation		672,000	115,000
Total deferred tax assets		33,892,000	16,074,000
Less valuation allowance		(31,361,000)	(15,207,000)
Net deferred tax assets		2,531,000	867,000
Deferred tax liabilities—depreciation and amortization		(2,501,000)	(867,000)
Unrealized gain on available-for-sale securities		(30,000)
Net deferred taxes		0	0
Change in the valuation allowance		16,200,000
Unrecognized tax benefits		$ 0	$ 0
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax computed at federal statutory tax rate	34.00%	34.00%	34.00%
State taxes, net of federal benefit	5.50%	5.60%	4.10%
General business credit carryovers	2.20%	4.20%	3.10%
Non‑deductible expenses	(5.00%)	(4.00%)	(15.50%)
Change in valuation allowance	(36.70%)	(40.20%)	(25.70%)
Effective income tax rate		(0.40%)
Tax Year 2033 | Federal
Income Tax Expense (Benefit), Continuing Operations, by Jurisdiction [Abstract]
Net operating loss carryforwards		$ 23,100,000
Tax Year 2033 | State
Income Tax Expense (Benefit), Continuing Operations, by Jurisdiction [Abstract]
Net operating loss carryforwards		20,400,000
Research and development tax credits carryforwards | Tax Year 2028 | Federal
Income Tax Expense (Benefit), Continuing Operations, by Jurisdiction [Abstract]
Tax credits carryforwards		3,100,000
Research and development tax credits carryforwards | Tax Year 2028 | State
Income Tax Expense (Benefit), Continuing Operations, by Jurisdiction [Abstract]
Tax credits carryforwards		$ 1,500,000