Lease termination (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($) ft²
Lease termination [Abstract]
Operating Leases, Income Statement, Sublease Revenue	$ 1.0
Area of Real Estate Property | ft²	17,100
Gain (Loss) on Contract Termination	$ 1.0
Gain (Loss) on Termination of Lease	0.2
Operating Leases, Future Minimum Payments Due	1.2
Operating Leases, Future Minimum Payments Receivable, Current	$ 0.4