Leases - Lease cost and other lease information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Lease Costs
Operating lease costs	$ 533
Variable lease costs	111
Short-term lease costs	15
Net lease cost	659	$ 700
Cash paid for amounts included in the measurement of lease liabilities
Operating lease cash flows – Fixed payments	513
Operating lease cash flows – Liability reduction	$ 463
Weighted average lease term (in years)	8 years 3 months 29 days
Weighted average discount rate (in percent)	3.11%