Leases - Lease cost and other lease information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Lease Costs
Operating lease costs	$ 619		$ 1,736
Variable lease costs	133		363
Short-term lease costs	46		69
Net lease cost	798	$ 600	2,168	$ 1,900
Cash paid for amounts included in the measurement of lease liabilities
Operating lease cash flows - Fixed payments	605		1,688
Operating lease cash flows - Liability reduction	526		1,479
Right of use assets obtained during the period in exchange for operating lease liabilities	$ 159		$ 923
Weighted average lease term (in years)	6 years 8 months 23 days		6 years 8 months 23 days
Weighted average discount rate (in percent)	3.04%		3.04%