Employee Benefit Plans - Components of Net Periodic Benefit Income for the Pension Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Retirement Benefits [Abstract]
Service cost	$ 3,101	$ 2,925	$ 6,142	$ 5,907
Interest cost	17,962	20,865	35,868	41,790
Expected return on plan assets	(38,858)	(38,410)	(77,590)	(76,933)
Amortization of prior service credit	172	173	344	346
Amortization of actuarial loss	12,509	11,088	24,965	22,210
Net periodic benefit income	$ (5,114)	$ (3,359)	$ (10,271)	$ (6,680)