Pension Plans and Other Postretirement Benefits Financial Assets Accounted for at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 583,659	$ 659,874
Pension Plans | Domestic Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	113,355	163,160
Pension Plans | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	114,554	130,935
Pension Plans | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	254,437	269,365
Pension Plans | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29,326
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	834	$ 2,232
Other Postretirement Benefits | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		834
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	450,766	493,848
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Plans | Domestic Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	111,665	160,976
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Plans | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	90,651	101,366
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Plans | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	219,124	231,506
Quoted Prices in Active Markets for Identical Items (Level 1) | Pension Plans | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29,326
Quoted Prices in Active Markets for Identical Items (Level 1) | Other Postretirement Benefits | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60,906	69,612
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Plans | Domestic Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,690	2,184
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Plans | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23,903	29,569
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Plans | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35,313	37,859
Quoted Prices in Active Markets for Similar Items (Level 2) | Pension Plans | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Quoted Prices in Active Markets for Similar Items (Level 2) | Other Postretirement Benefits | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		834
Unobservable Inputs (Level 3) | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Unobservable Inputs (Level 3) | Pension Plans | Domestic Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Unobservable Inputs (Level 3) | Pension Plans | International Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Unobservable Inputs (Level 3) | Pension Plans | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Unobservable Inputs (Level 3) | Pension Plans | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Unobservable Inputs (Level 3) | Other Postretirement Benefits | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
Absolute Return Measured at Net Asset Value | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 71,987	$ 96,414