Leases - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Components of lease expense
Operating lease cost	$ 1,317		$ 2,432
Operating lease cost		$ 740		$ 1,431
Finance lease cost
Amortization of leased assets	147		409
Amortization of leased assets		262		588
Interest on lease liabilities	11		27
Interest on lease liabilities		31		70
Total finance lease cost	158		436
Total finance lease cost		293		658
Total lease cost	$ 1,475		$ 2,868
Total lease cost		$ 1,033		$ 2,089