Leases - Components of lease expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Finance lease cost:
Amortization of assets	$ 1,039	$ 1,019	$ 2,077	$ 1,405
Interest on lease liabilities	482	454	971	699
Operating lease expense:
Operating lease cost	2,239	2,324	4,502	4,594
Variable lease cost	268	219	532	429
Sublease income	(47)	(46)	(95)	(93)
Total lease costs	$ 3,981	$ 3,970	$ 7,987	$ 7,034