Pension Plans - Components of Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Retirement Benefits [Abstract]
Service cost	$ 7,722	$ 7,747	$ 22,803	$ 23,513
Interest cost	1,281	1,297	3,774	3,926
Expected return on plan assets	(1,420)	(1,585)	(4,175)	(4,798)
Recognized actuarial gain	14	(94)	42	(282)
Net periodic pension cost	$ 7,597	$ 7,365	$ 22,444	$ 22,359