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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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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Amount, after accumulated amortization, of debt discount (premium).

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Represents the aggregate of total long-term debt, including current maturities and short-term debt.

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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 - Schedule of Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Oct. 31, 2017	Sep. 30, 2017	Jul. 30, 2016
Debt Instrument [Line Items]
Unamortized debt premium, net	$ (3,220)		$ (3,413)
Debt issuance costs	16,545		14,800
Total debt, net	1,324,509		1,327,412
Senior Notes
Debt Instrument [Line Items]
Unamortized debt premium, net	(3,220)		(3,413)
Debt issuance costs	16,545		14,800
Total debt, net	$ 1,257,902		1,259,840
Senior Notes \| 5 7/8% Unsecured Senior Notes Maturing October 2027
Debt Instrument [Line Items]
Debt instrument, face amount		$ 400,000
Stated interest rate on debt instrument (percent)		5.875%
Senior Notes \| 5 3/4% Senior Notes Maturing June 2019
Debt Instrument [Line Items]
Stated interest rate on debt instrument (percent)	5.75%
Total debt, net	$ 96,393		$ 321,393
Senior Notes \| 7 1/2% Senior Notes Maturing September 2021
Debt Instrument [Line Items]
Stated interest rate on debt instrument (percent)	7.50%		7.50%
Senior Notes \| 8 3/4% Senior Notes Maturing March 2022
Debt Instrument [Line Items]
Stated interest rate on debt instrument (percent)	8.75%		8.75%
Total debt, net	$ 500,000		$ 500,000
Senior Notes \| 7 1/4% Senior Notes Maturing February 2023
Debt Instrument [Line Items]
Stated interest rate on debt instrument (percent)	7.25%		7.25%
Total debt, net	$ 24,834		$ 199,834
Senior Notes \| 6 3/4% Senior Notes Maturing March of 2025
Debt Instrument [Line Items]
Stated interest rate on debt instrument (percent)	6.75%		6.75%
Total debt, net	$ 250,000		$ 250,000
Senior Notes \| 5 7/8% Senior Notes Maturing October 2027
Debt Instrument [Line Items]
Stated interest rate on debt instrument (percent)	5.875%		0.00%
Total debt, net	$ 400,000
Junior Subordinated Notes
Debt Instrument [Line Items]
Stated interest rate on debt instrument (percent)				7.987%
Total debt, net	62,453		$ 61,937
Other Secured Notes payable
Debt Instrument [Line Items]
Total debt, net	$ 4,154		$ 5,635