Principal Business Activity and Significant Accounting Policies - Recent accounting pronouncements (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Abstract]
Accumulated deficit	$ (3,493)
Recast | ASU 2016-02
Revenue, Initial Application Period Cumulative Effect Transition [Abstract]
Operating lease liabilities	1,700
Right-of-use asset	$ 1,700