Pension Plans and Other Postretirement Benefits Financial Assets Accounted for at Fair Value on Recurring Basis (Details) - Pension Plans - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 638,149	$ 583,659
Domestic Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	119,842	113,355
International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	126,828	114,554
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	317,667	254,437
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		29,326
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35
Quoted Prices in Active Markets for Identical Items (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	493,267	450,766
Quoted Prices in Active Markets for Identical Items (Level 1) | Domestic Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	118,255	111,665
Quoted Prices in Active Markets for Identical Items (Level 1) | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	95,246	90,651
Quoted Prices in Active Markets for Identical Items (Level 1) | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	279,731	219,124
Quoted Prices in Active Markets for Identical Items (Level 1) | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		29,326
Quoted Prices in Active Markets for Identical Items (Level 1) | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35
Quoted Prices in Active Markets for Similar Items (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	71,105	60,906
Quoted Prices in Active Markets for Similar Items (Level 2) | Domestic Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,587	1,690
Quoted Prices in Active Markets for Similar Items (Level 2) | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31,582	23,903
Quoted Prices in Active Markets for Similar Items (Level 2) | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37,936	35,313
Quoted Prices in Active Markets for Similar Items (Level 2) | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Quoted Prices in Active Markets for Similar Items (Level 2) | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Unobservable Inputs (Level 3) | Domestic Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Unobservable Inputs (Level 3) | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Unobservable Inputs (Level 3) | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Unobservable Inputs (Level 3) | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Unobservable Inputs (Level 3) | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Absolute Return Measured at Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 73,777	$ 71,987