Debt (Schedule of Obligations Under Debt Arrangements) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Senior secured credit facility	$ 1,372,500	$ 1,278,200
Unamortized Debt Issuance Expense and Discounts (Premiums)	41,951	36,831
Senior unsecured notes	2,358,049	1,813,169
Long-term debt, Face Values	3,772,500	3,128,200
Total long-term debt	$ 3,730,549	$ 3,091,369
5.750% senior unsecured notes due February 2021
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	5.75%	5.75%
Debt Instrument, Face Amount	$ 350,000	$ 350,000
Unamortized Debt Issuance Expense and Discounts (Premiums)	3,399	4,163
Senior unsecured notes	$ 346,601	$ 345,837
6.750% senior unsecured notes due August 2022
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	6.75%	6.75%
Debt Instrument, Face Amount	$ 750,000	$ 750,000
Unamortized Debt Issuance Expense and Discounts (Premiums)	16,889	19,296
Senior unsecured notes	$ 733,111	$ 730,704
6.000% senior unsecured notes due May 2023
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	6.00%	6.00%
Debt Instrument, Face Amount	$ 400,000	$ 400,000
Unamortized Debt Issuance Expense and Discounts (Premiums)	5,958	6,758
Senior unsecured notes	$ 394,042	$ 393,242
5.625% senior unsecured notes due June 2024
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	5.625%	5.625%
Debt Instrument, Face Amount	$ 350,000	$ 350,000
Unamortized Debt Issuance Expense and Discounts (Premiums)	5,941	6,614
Senior unsecured notes	$ 344,059	$ 343,386
6.500% senior unsecured notes due October 2025
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	6.50%	6.50%
Debt Instrument, Face Amount	$ 550,000	$ 0
Unamortized Debt Issuance Expense and Discounts (Premiums)	9,764	0
Senior unsecured notes	540,236	0
Credit Facility [Domain]
Debt Instrument [Line Items]
Unamortized Debt Issuance Expense and Discounts (Premiums)	$ 0	$ 0

Long-term debt, Face Values before unamortized discount and debt issuance costs

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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. Also includes the amount of debt discount (premium) that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

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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- Definition

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
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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.

+ References

No definition available.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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- Definition

Carrying amount of collateralized debt obligations with maturities initially due after one year or beyond the operating cycle, if longer, excluding the current portion. Obligations include, but not limited to, mortgage loans, chattel loans, and other borrowings secured by assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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- Definition

Carrying value as of the balance sheet date of uncollateralized debt obligation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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