Employee Benefits - Summary of Components of Net Pension Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Components of net periodic benefit cost:
Service cost	$ 7,898	$ 6,231	$ 15,794	$ 12,463
Interest cost	1,267	2,615	2,536	5,232
Expected return on plan assets	(8,141)	(7,425)	(16,283)	(14,850)
Past service cost	(2,945)	6	(5,890)	12
Recognized net actuarial loss	3,538	2,361	7,075	4,721
Net periodic benefit cost	$ 1,617	$ 3,788	$ 3,232	$ 7,578