Employee Benefit Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1,194	$ 1,015	$ 3,780	$ 3,236
Interest cost	2,525	3,729	7,595	11,247
Expected return on plan assets	(4,627)	(4,899)	(13,891)	(14,722)
Amortization of prior service cost (credit)	54	37	275	123
Recognized actuarial loss (gain)	2,832	2,355	8,401	7,070
Settlement loss	3,375	0	3,375	0
Net periodic benefit cost (credit)	5,353	2,237	9,535	6,954
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost	19	35	59	104
Amortization of prior service cost (credit)	(509)	(509)	(1,528)	(1,528)
Recognized actuarial loss (gain)	(2)	(19)	(7)	(56)
Net periodic benefit cost (credit)	$ (492)	$ (493)	$ (1,476)	$ (1,480)