Employee Benefit Plans - Net periodic benefit costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 256	$ 267
Interest cost	4,069	4,151
Recognized actuarial loss	1,546	2,625
Expected return on plan assets	(7,511)	(7,339)
Prior service cost	55
Net periodic benefit cost	$ (1,585)	$ (296)