Pension Benefits and Other Postretirement Benefits (Additional Information) (Details)		2 Months Ended		3 Months Ended				9 Months Ended		12 Months Ended
	Oct. 17, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) plan	Jul. 27, 2020 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of qualified noncontributory defined benefit plans | plan										2
Pension surplus investment balance		$ 12,790,000	$ 12,790,000	$ 4,337,000		$ 12,790,000		$ 4,337,000		$ 12,790,000
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contributions				0			$ 0	0	$ 0
Pension Benefits | Merged Plan
Defined Benefit Plan Disclosure [Line Items]
Payment for settlement	$ 123,300,000		$ 1,300,000
Lump sum distributions		$ 38,900,000
Settlement charge					$ 0	$ 53,200,000
Pension surplus investment balance				9,300,000				9,300,000			$ 7,400,000
Contributions									$ 0
Pension Benefits | Union Plan
Defined Benefit Plan Disclosure [Line Items]
Contributions				0
Additional contributions required to make for remainder of fiscal year				$ 0				$ 0