Leases - Lease right-of-use assets and liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Lease Right-of-Use Assets
Operating lease right-of-use assets	$ 7,965	$ 8,343
Finance lease right-of-use assets	$ 289	$ 318
Finance Lease, Right-of-Use Asset, balance sheet location	us-gaap:PropertyPlantAndEquipmentNet	us-gaap:PropertyPlantAndEquipmentNet
Lease right-of-use assets	$ 8,254	$ 8,661
Operating lease liabilities	8,480	8,864
Finance lease liabilities	$ 589	$ 640
Finance lease liabilities, balance sheet location	us-gaap:LongTermDebt	us-gaap:LongTermDebt
Lease liabilities	$ 9,069	$ 9,504