Leases - Operating lease costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Leases [Abstract]
Operating lease cost	$ 2,700	$ 2,962	$ 2,686
Finance lease cost:
Amortization of right-of-use assets - finance leases	369	0	0
Interest expense on finance leases	568	0	0
Operating cash flows from operating leases	1,969	2,354	2,103
Operating cash flows from finance leases	$ 533	$ 0	$ 0