Leases - Supplemental balance sheet information (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019
Operating Leases:
Operating lease right-of-use asset	$ 6,295	$ 7,500
Financial position	us-gaap:OperatingLeaseRightOfUseAsset
Operating lease liability - current	$ 1,209
Financial position	us-gaap:OperatingLeaseLiabilityCurrent
Operating lease liability - noncurrent	$ 6,293
Financial position	us-gaap:OperatingLeaseLiabilityNoncurrent
Total operating lease liabilities	$ 7,502
Financial position	us-gaap:OperatingLeaseLiabilityCurrent us-gaap:OperatingLeaseLiabilityNoncurrent