Other Postretirement Benefit Plans - Change in Benefit Obligation, Plan Assets, Funded Status, and Balance Sheet Items (Details) - Accrued postretirement liability - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Benefit obligation at beginning of year		$ 63,400,000	$ 186,900,000
Service cost		200,000	200,000	$ 200,000
Interest cost		2,100,000	5,900,000	7,600,000
Plan amendments	$ (92,800,000)	(3,100,000)	(92,800,000)
Actuarial losses (gains)		1,800,000	(14,400,000)
International plan exchange rate change		0	200,000
Benefits paid		(6,800,000)	(22,700,000)
Acquisitions		0	100,000
Benefit obligation at end of year		$ 57,600,000	$ 63,400,000	$ 186,900,000