Pension Plans - Components of Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Retirement Benefits [Abstract]
Service cost	$ 7,536	$ 7,977
Interest cost	1,247	1,324
Expected return on plan assets	(1,374)	(1,618)
Recognized actuarial gain	14	(94)
Net periodic pension cost	$ 7,423	$ 7,589