Debt - 1.0% Convertible Debentures due 2035 (Details) shares in Millions	1 Months Ended		3 Months Ended
	Dec. 31, 2015 USD ($) day	Jun. 30, 2015 USD ($)	Dec. 31, 2021 USD ($) day shares	Sep. 30, 2021 USD ($) shares	Jun. 30, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 07, 2015	Oct. 24, 2011
Debt Instrument [Line Items]
Face value			$ 889,400,000	$ 918,000,000
Trading days | day			20
Consecutive trading days | day			30
Repayments of convertible debt			$ 28,646,000			$ 0
Loss on extinguishment of debt			215,000			$ 0
Total before unamortized discount			$ 889,392,000
Convertible Debentures 1.0% Due 2035
Debt Instrument [Line Items]
Stated percentage	1.00%		1.00%				1.00%
Face value	$ 676,500,000
Debt proceeds	663,800,000
Repurchased face amount	$ 472,500,000		$ 2,300,000	89,200,000	$ 457,000,000
Trading days | day	10
Contingent interest amount per principal	$ 1,200
Accrued interest rate	0.50%
Long-term debt	$ 495,400,000
Debt recorded as additional paid-in capital	$ 181,100,000
Conversion ratio	0.0414576
Consecutive business days | day	5
Consecutive trading days | day	5
Redemption price percentage	100.00%
Percentage of principal amount redeemable	100.00%
Repayments of convertible debt			$ 2,300,000	$ 89,200,000	$ 5,000,000
Shares converted (in shares) | shares			0.1	2.1	18.9
Debt repurchase allocation, debt portion			$ 2,200,000	$ 85,400,000	$ 435,100,000
Debt repurchase allocation - Equity portion			3,100,000	117,600,000	567,100,000
Unamortized discount write-off			100,000	5,600,000	32,400,000
Write-off of unamortized costs				300,000	1,400,000
Loss on extinguishment of debt			0	2,100,000	15,000,000
Inducement expense					3,100,000
Interest expense earned					1,900,000
Value of common stock consideration			3,000,000	$ 113,800,000	$ 1,002,200,000
Total before unamortized discount			128,000,000
Reclassification from permanent equity to mezzanine equity			5,800,000
Convertible Debentures 1.0% Due 2035 | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Repurchased face amount			$ 23,500,000
Shares converted (in shares) | shares			0.5
Repurchase amount			$ 23,500,000
Converted amount			$ 53,800,000
Senior Convertible Debentures due in 2031
Debt Instrument [Line Items]
Stated percentage								2.75%
Repurchased face amount	$ 38,300,000
Repayments of convertible debt		$ 256,200,000
Minimum | Convertible Debentures 1.0% Due 2035
Debt Instrument [Line Items]
Percentage of stock closing price to debt conversion price	130.00%
Number of trading days	20 days		20 days
Maximum | Convertible Debentures 1.0% Due 2035
Debt Instrument [Line Items]
Percentage of stock closing price to debt conversion price	98.00%
Number of trading days	30 days		30 days
Principal amount per note	$ 1,000
If-converted value exceeding principal amount			$ 165,500,000