Postretirement Benefits - Pension Liability (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Pension benefit obligation	$ 588,269	$ 562,567
Qualified Plan | Pension plans | Funded defined benefit pension
Defined Benefit Plan Disclosure [Line Items]
Pension benefit obligation	517,770	492,103
Nonqualified Plan | SERP
Defined Benefit Plan Disclosure [Line Items]
Pension benefit obligation	$ 70,499	$ 70,464