Employee Retirement Plans and Postretirement Benefits - Defined Contribution Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Retirement Plans and Postretirement Benefits
Defined Contribution Plan, vesting period	4 years
Matching contributions	50.00%
Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Defined Contribution Plan, Cost	$ 1.6	$ 1.4	$ 1.1