Credit Facilities and Debt 1.50% Convertible Debentures due 2035 (Details) - USD ($)	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Mar. 31, 2020	Nov. 01, 2017	Dec. 07, 2015	Jun. 01, 2015	Oct. 24, 2011
Debt Instrument [Line Items]
Long-term debt, face value				$ 1,666,500,000	$ 2,137,000,000.0
Debt Issuance Costs, Noncurrent, Net				$ 451,000	$ 511,000
Convertible Debentures One Percent Due Twenty Thirty Five [Member]
Debt Instrument [Line Items]
Long-term debt, face value									$ 676,500,000
Convertible debentures, interest rate				1.00%	1.00%				1.00%
Proceeds from long-term debt, net of issuance costs					$ 663,800,000
Convertible Debt, Noncurrent									$ 495,400,000
Debt Instrument, Convertible, Carrying Amount of Equity Component									$ 181,100,000
Debt Instrument, Unamortized Discount				$ 91,600,000	$ 116,900,000
Debt Instrument, Convertible, Conversion Price									$ 24.12
Convertible Debentures One Point Five Percent Due November One Twenty Thirty Five [Member] [Member]
Debt Instrument [Line Items]
Unamortized Loss Reacquired Debt, Noncurrent							$ 2,500,000
Debt Instrument, Repurchase Amount							41,300,000
debt issuance cost write off							100,000
loss on extinguishment of debt							800,000
Debtor-in-Possession Financing, Borrowings Outstanding						$ 227,400,000
Long-term debt, face value										$ 263,900,000
Convertible debentures, interest rate				1.50%	1.50%
debt instrument net proceeds										$ 253,200,000
Debt issuance Percentage of Principal Amount										97.09%
Debt Instrument, Unamortized Discount (Premium), Net										$ 7,700,000
Convertible Debt, Noncurrent										208,600,000
Debt Instrument, Convertible, Carrying Amount of Equity Component										$ 55,300,000
Debt Instrument, Unamortized Discount				$ 22,700,000	$ 32,800,000
Debt Instrument, Convertible, Conversion Price										$ 20.61
Aggregate Principal Amount of Senior Notes, Redemption Price, Percentage				100.00%
Debt Instrument, Repurchased Face Amount							36,500,000
debt repurchase allocation - Debt portion							34,700,000
Debt repurchase allocation - Equity portion							$ 6,600,000
2.75% Convertible Debentures due November 1, 2031
Debt Instrument [Line Items]
Long-term debt, face value								$ 46,600,000	$ 395,500,000		$ 690,000,000.0
Convertible debentures, interest rate			2.75%	2.75%	2.75%						2.75%
Repayments of Convertible Debt	$ 331,200,000	$ 256,200,000	$ 38,300,000	$ 17,800,000	$ 38,300,000
debt instrument net proceeds											$ 676,100,000
Convertible Debt, Noncurrent											533,600,000
Debt Instrument, Convertible, Carrying Amount of Equity Component											$ 156,400,000
Debt Instrument, Unamortized Discount				$ 0	0
Principal Amount Per Note Used In Conversion Rate					$ 1,000
Minimum | Convertible Debentures One Percent Due Twenty Thirty Five [Member]
Debt Instrument [Line Items]
Ratio of Common Stock Closing Price to Debt Conversion Price, Percentage									130.00%
Debt Instrument Conversion Circumstance Number Of Trading Days					20 days
Minimum | Convertible Debentures One Point Five Percent Due November One Twenty Thirty Five [Member] [Member]
Debt Instrument [Line Items]
Ratio of Common Stock Closing Price to Debt Conversion Price, Percentage					130.00%
Debt Instrument Conversion Circumstance Number Of Trading Days				20 days
Maximum | Convertible Debentures One Percent Due Twenty Thirty Five [Member]
Debt Instrument [Line Items]
Ratio of Common Stock Closing Price to Debt Conversion Price, Percentage									98.00%
Debt Instrument Conversion Circumstance Number Of Trading Days					30 days
Principal Amount Per Note Used In Conversion Rate									$ 1,000
Maximum | Convertible Debentures One Point Five Percent Due November One Twenty Thirty Five [Member] [Member]
Debt Instrument [Line Items]
Ratio of Common Stock Closing Price to Debt Conversion Price, Percentage					98.00%
After auto spin-off [Member] | Convertible Debentures One Percent Due Twenty Thirty Five [Member]
Debt Instrument [Line Items]
Convertible debt shares per $1,000 principal amount									41.4576
After auto spin-off [Member] | Convertible Debentures One Point Five Percent Due November One Twenty Thirty Five [Member] [Member]
Debt Instrument [Line Items]
Convertible debt shares per $1,000 principal amount										48.5216
Ending on Last Trading Day of Previous Fiscal Quarter [Member] | Convertible Debentures One Point Five Percent Due November One Twenty Thirty Five [Member] [Member]
Debt Instrument [Line Items]
Debt Instrument Conversion Circumstance Number Of Consecutive Trading Days				30 days
Before auto spin-off [Member] | Convertible Debentures One Percent Due Twenty Thirty Five [Member]
Debt Instrument [Line Items]
Convertible debt shares per $1,000 principal amount									36.7360
Before auto spin-off [Member] | Convertible Debentures One Point Five Percent Due November One Twenty Thirty Five [Member] [Member]
Debt Instrument [Line Items]
Convertible debt shares per $1,000 principal amount										42.9978