Components of Net Pension Benefit Loss/(Gain) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Retirement Benefits [Abstract]
Interest and service cost	$ 1,762	$ 1,995	$ 3,524	$ 3,990
Expected return on plan assets	(2,640)	(3,443)	(5,280)	(6,886)
Amortization of net loss	878	826	1,756	1,652
Net periodic loss/(benefit)		$ (622)		$ (1,244)