Leases - Supplemental unaudited consolidated balance sheet information (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Supplemental unaudited consolidated balance sheet information
Operating lease right-of-use assets	$ 11,356	$ 10,580
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Operating lease right-of-use assets	Operating lease right-of-use assets
Operating lease liabilities current	$ 2,855	$ 2,636
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Accrued Liabilities, Current	Other Accrued Liabilities, Current
Operating lease liabilities noncurrent	$ 12,399	$ 11,299
Total lease liabilities	$ 15,254	$ 13,935