Pension Benefits - Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Fair Value of Plan Assets	$ 205,463	$ 184,758	$ 190,534	$ 178,375
Minimum
Pension Benefits
Redemption notice	65 days
Maximum
Pension Benefits
Redemption notice	90 days
Large-Cap Disciplined Equity
Pension Benefits
Fair Value of Plan Assets	$ 6,844	15,894
International Equity
Pension Benefits
Fair Value of Plan Assets	35,962	22,022
Long Duration Fixed Income
Pension Benefits
Fair Value of Plan Assets	133,592	109,408
High Yield
Pension Benefits
Fair Value of Plan Assets		4,965
Emerging Markets Debt
Pension Benefits
Fair Value of Plan Assets		4,566
Other Investments
Pension Benefits
Fair Value of Plan Assets	29,065	27,903
Quoted Prices in Active Markets for Identical Assets (Level 1)
Pension Benefits
Fair Value of Plan Assets	176,398	156,855
Quoted Prices in Active Markets for Identical Assets (Level 1) | Large-Cap Disciplined Equity
Pension Benefits
Fair Value of Plan Assets	6,844	15,894
Quoted Prices in Active Markets for Identical Assets (Level 1) | International Equity
Pension Benefits
Fair Value of Plan Assets	35,962	22,022
Quoted Prices in Active Markets for Identical Assets (Level 1) | Long Duration Fixed Income
Pension Benefits
Fair Value of Plan Assets	133,592	109,408
Quoted Prices in Active Markets for Identical Assets (Level 1) | High Yield
Pension Benefits
Fair Value of Plan Assets		4,965
Quoted Prices in Active Markets for Identical Assets (Level 1) | Emerging Markets Debt
Pension Benefits
Fair Value of Plan Assets		4,566
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Investments
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Observable Inputs (Level 2)
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Observable Inputs (Level 2) | Large-Cap Disciplined Equity
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Observable Inputs (Level 2) | International Equity
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Observable Inputs (Level 2) | Long Duration Fixed Income
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Observable Inputs (Level 2) | High Yield
Pension Benefits
Fair Value of Plan Assets		0
Significant Observable Inputs (Level 2) | Emerging Markets Debt
Pension Benefits
Fair Value of Plan Assets		0
Significant Observable Inputs (Level 2) | Other Investments
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Unobservable Inputs (Level 3)
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Unobservable Inputs (Level 3) | Large-Cap Disciplined Equity
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Unobservable Inputs (Level 3) | International Equity
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Unobservable Inputs (Level 3) | Long Duration Fixed Income
Pension Benefits
Fair Value of Plan Assets	0	0
Significant Unobservable Inputs (Level 3) | High Yield
Pension Benefits
Fair Value of Plan Assets		0
Significant Unobservable Inputs (Level 3) | Emerging Markets Debt
Pension Benefits
Fair Value of Plan Assets		0
Significant Unobservable Inputs (Level 3) | Other Investments
Pension Benefits
Fair Value of Plan Assets	$ 0	$ 0