Employee Benefit Plans - Components of Net Periodic Benefit Income for the Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Retirement Benefits [Abstract]
Service cost	$ 3,041	$ 2,982
Interest cost	17,906	20,925
Expected return on plan assets	(38,732)	(38,523)
Amortization of prior service cost	172	173
Amortization of actuarial loss	12,456	11,122
Net periodic benefit income	$ (5,157)	$ (3,321)