Employee Benefit Plans - Components of Net Periodic Pension/Postretirement Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Settlement expense			$ 19,900
Pension plans
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligations			305
Expected return on plan assets			(835)
Amortization of net loss			262
Settlement expense			19,900
Net periodic pension/postretirement benefit cost			19,632
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	$ 103	$ 103	124
Interest cost on projected benefit obligations	154	210	189
Amortization of actuarial gain	(22)	(117)	(30)
Amortization of prior service credit			(13)
Net periodic pension/postretirement benefit cost	$ 235	$ 196	$ 270