The percentage of the premium over the stock price of the conversion feature embedded in the debt instrument.

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Carrying amount of debt component of the debt issuance costs.

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Carrying amount of equity component of the debt issuance costs.

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The available increase in borrowing capacity of the debt instrument under certain circumstances.

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The sub-limit within the overall line of credit capacity that is available for letters of credit.

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Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount of amortization expense attributable to debt issuance costs.

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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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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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No definition available.

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The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

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

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

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

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Percentage of principal amount of debt redeemed.

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No definition available.

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Amount, after accumulated amortization, of debt discount.

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

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Represents the portion of interest incurred in the period on debt arrangements that was charged against earnings, excluding amortization of debt discount (premium) and financing costs.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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No definition available.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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Borrowings (Details) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
Borrowings (Details) $ / shares in Units, $ in Thousands	Sep. 30, 2020 USD ($) item $ / shares	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) item	Apr. 30, 2019 USD ($)	Feb. 28, 2017 USD ($)
Borrowings
Borrowings outstanding	$ 51,000		$ 59,000
Revolving Credit Facility
Borrowings
Maximum borrowing capacity				$ 535,000
Sub-limit available for letters of credit				300,000
Unused commitment fee (as a percent)	0.10%
Amount outstanding under letters of credit	$ 75,400
Available credit facility	$ 408,600
Revolving Credit Facility \| Minimum
Borrowings
Unused commitment fee (as a percent)	0.10%
Revolving Credit Facility \| Maximum
Borrowings
Increase in the credit agreement's borrowing capacity available under certain circumstances				$ 250,000
Unused commitment fee (as a percent)	0.25%
Revolving Credit Facility \| LIBOR
Borrowings
Interest rate margin (as a percent)	1.00%
Revolving Credit Facility \| LIBOR \| Minimum
Borrowings
Interest rate margin (as a percent)	1.00%
Revolving Credit Facility \| LIBOR \| Maximum
Borrowings
Interest rate margin (as a percent)	1.75%
1.25% Convertible Senior Notes Due 2022
Borrowings
Principal amount	$ 287,500				$ 287,500
Interest rate (as a percentage)	1.25%				1.25%
Conversion ratio	9.3056
Conversion price \| $ / shares	$ 107.46
Premium on stock price	38.50%
Threshold percentage of stock price	130.00%		130.00%
Number of trading days \| item	20		20
Number of consecutive trading days \| item	30		30
Principal amount of the notes to be repurchased (as a percentage)	100.00%
Liability component of convertible debt	$ 242,400
Equity component of convertible debt	45,100
Debt issuance costs	7,700
Debt Component of debt issuance costs	6,500
Equity component of debt issuance costs	1,200
Total interest expense	3,300	$ 3,200
Contractual interest expense	900	900
Amortization of debt discount	2,100	2,000
Amortization of debt issuance costs	300	$ 300
Unamortized discount	16,969		$ 19,075
Unamortized debt issuance costs	$ 2,253		$ 2,547
Effective interest rate (as a percent)	4.50%
Bank lines of credit
Borrowings
Amount outstanding under letters of credit	$ 57,400
Available credit facility	$ 14,700