Pension Benefits - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($)	Dec. 31, 2017
Pension Benefits
Normal retirement age (in years)	65 years
Early retirement age, low end of range (in years)	55 years
Early retirement age, high end of range (in years)	64 years
Attainment of credited service (in years)	10 years
Threshold age for reduction in early retirement benefit (in years)	62 years
Number of highest consecutive period of average compensation, used in plan benefit calculation (in years)	5 years
Period of average compensation, used in plan benefit calculation (in years)	10 years
Funded status (deficit)	$ (16.0)	$ (17.0)
AOCI, defined benefit plan, after tax	56.1	49.9
AOCI, defined benefit plan, tax	(6.8)	$ (8.8)
Estimated amount to be amortized from AOCI	$ 1.0
Number of a high grade bonds considered when selecting discount rate | item	500
Expected return on plan assets	7.25%	7.25%	7.25%
Domestic equity securities
Pension Benefits
Target allocation, percent	3.00%
Fixed income securities
Pension Benefits
Target allocation, percent	65.00%
International Equity
Pension Benefits
Target allocation, percent	18.00%
Alternatives
Pension Benefits
Target allocation, percent	14.00%