Employee Benefits - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Payment for Other Postretirement Benefits		$ 1,700,000	$ 2,900,000
Warrick | Accrued Salaries, Wages and Related Expenses
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 1,100,000
Postretirement Health Coverage | Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Maximum contribution threshold				$ 2,900,000
Payment for Other Postretirement Benefits	1,700,000
Pension Plan | Warrick
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	6,500,000
Expected minimum employer contributions in 2021	100,000
Other Postretirement Benefits Plan | Warrick
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	78,100,000
Expected minimum employer contributions in 2021	$ 700,000
Level 2 | Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of deferred compensation assets		10,300,000		$ 9,600,000
Accrued salaries, wages and related expenses
Defined Benefit Plan Disclosure [Line Items]
Accrued salaries, wages and related expenses		$ 6,700,000