Pension Plans - Components of Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Retirement Benefits [Abstract]
Service cost	$ 6,548	$ 7,722	$ 20,083	$ 22,803
Interest cost	1,199	1,281	3,682	3,774
Expected return on plan assets	(1,384)	(1,420)	(4,247)	(4,175)
Recognized actuarial loss	32	14	96	42
Net periodic pension cost	$ 6,395	$ 7,597	$ 19,614	$ 22,444