Summary of significant accounting policies - Recently issue accounting Pronouncement (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease ROU asset	$ 226	$ 280
Operating lease liabilities, current (included in accrued expenses and other current liabilities)	$ 230	224
Deferred rent, current (included in accrued expenses and other current liabilities)			$ 2
Operating lease liabilities, noncurrent (included in other liabilities)		60
Deferred rent, noncurrent (included in other liabilities			$ 2
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease ROU asset		280
Operating lease liabilities, current (included in accrued expenses and other current liabilities)		224
Deferred rent, current (included in accrued expenses and other current liabilities)		(2)
Operating lease liabilities, noncurrent (included in other liabilities)		60
Deferred rent, noncurrent (included in other liabilities		$ (2)