Employee Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension
Components of Net Periodic Benefit Cost
Service cost	$ 9,857	$ 11,663	$ 5,646
Interest cost	36,138	35,499	15,926
Expected return on plan assets	(52,343)	(57,438)	(25,978)
Amortization of prior service (credit) cost	569	572	761
Amortization of losses	10,363	11,648	11,651
Pension settlement loss	8,787	0	0
Net periodic benefit cost	13,371	1,944	8,006
Postretirement
Components of Net Periodic Benefit Cost
Service cost	1,849	1,716	1,249
Interest cost	1,432	1,327	827
Expected return on plan assets	0	0	0
Amortization of prior service (credit) cost	(153)	(153)	(151)
Amortization of losses	81	229	333
Pension settlement loss	0	0	0
Net periodic benefit cost	$ 3,209	$ 3,119	$ 2,258