Carrying amount of long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months or greater than the normal operating cycle, if longer. The debt is convertible into another form of financial instrument, typically the entity's common stock.

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The price per share of the conversion feature embedded in the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Debt and Credit Facilities 1.0% Convertible Debentures due 2035 (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended			6 Months Ended
	Nov. 30, 2017	Mar. 31, 2018	Jun. 30, 2015	Dec. 31, 2014	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2018	Dec. 07, 2015	Jun. 01, 2015	Oct. 24, 2011
Debt Instrument [Line Items]
Debt Instrument, Face Amount					$ 2,137,000		$ 2,437,000
Debt Issuance Costs, Noncurrent, Net					677		$ 843
Loss on extinguishment of debt					$ 910	$ 0
Convertible Debentures One Percent Due Twenty Thirty Five [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount								$ 676,500
Debt Instrument, Convertible, Carrying Amount of Equity Component								$ 181,100
Debt Instrument, Convertible, Conversion Price								$ 27.22
Debt Instrument, Interest Rate, Stated Percentage					1.00%		1.00%	1.00%
Convertible Debt, Noncurrent								$ 495,400
Convertible Debentures Two Point Seven Five Percent Due November One Twenty Thirty One [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount					$ 46,600					$ 690,000
Debt Instrument, Convertible, Carrying Amount of Equity Component										$ 156,400
Debt Instrument, Convertible, Conversion Price										$ 32.30
Repayments of Convertible Debt		$ 17,800	$ 256,200	$ 38,300		$ 17,800
Debt Instrument, Interest Rate, Stated Percentage					2.75%		2.75%			2.75%
Repayments of Debt	$ 331,200	$ 331,200
Convertible Debt, Noncurrent										$ 533,600
Convertible Debentures One Point Five Percent Due November One Twenty Thirty Five [Member] [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount									$ 263,900
Debt Instrument, Convertible, Carrying Amount of Equity Component									$ 55,300
Debt Instrument, Convertible, Conversion Price									$ 23.26
Debt Instrument, Interest Rate, Stated Percentage					1.50%		1.50%
Convertible Debt, Noncurrent									$ 208,600