Debt - Senior Notes due 2023 (Details) - Senior Notes - Senior Notes Due 2023 - USD ($)	Feb. 25, 2015	Sep. 30, 2016
Debt Instrument [Line Items]
Debt instrument, principal amount	$ 700,000,000
Debt instrument, interest rate	6.50%
Percentage of principal, issue price	100.00%
Debt issuance costs	$ 7,000,000
Unamortized debt issuance fees	$ 1,800,000
Carrying value of debt		$ 693,000,000
Redemption scenario 1
Debt Instrument [Line Items]
Percentage of principal redeemed	40.00%
Percentage of principal amount, redemption price	106.50%
Redemption scenario 2
Debt Instrument [Line Items]
Percentage of principal amount, redemption price	100.00%
Redemption scenario 3
Debt Instrument [Line Items]
Percentage of principal amount, redemption price	101.00%

Debt Instrument, Issue Price, Percentage of Principal

No definition available.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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-Publisher FASB
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-Topic 835
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-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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- Definition

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

+ References

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- Definition

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.

+ References

No definition available.

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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
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- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

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- Definition

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

+ References

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-Publisher FASB
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-Topic 835
-SubTopic 30
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-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68176171&loc=SL68176184-208336

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
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- Definition

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.

+ References

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