Leases - Components of lease expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Finance lease cost:
Amortization of assets	$ 4,150	$ 3,535
Interest on lease liabilities	1,915	1,693
Operating lease expense:
Operating lease cost	9,012	9,102
Variable lease cost	1,072	1,109
Sublease income	(193)	(187)
Total lease costs	$ 15,956	$ 15,252