Retirement Plans - Net Pension Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Net pension expense	$ 107,447	$ 666	$ 131,227	$ 1,996