Debt (Schedule of Obligations Under Debt Arrangements) (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018	Dec. 11, 2017
Debt Instrument [Line Items]
Senior secured credit facility	$ 967,000,000	$ 970,100,000
Unamortized debt issuance expense and discounts (premiums)	33,863,000	37,637,000
Senior unsecured notes, net of debt issuance costs	2,466,137,000	2,462,363,000
Total long-term debt, principal	3,467,000,000	3,470,100,000
Total long-term debt	$ 3,433,137,000	$ 3,432,463,000
6.750% senior unsecured notes
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	6.75%	6.75%
Principal	$ 750,000,000	$ 750,000,000
Unamortized debt issuance expense and discounts (premiums)	11,069,000	12,763,000
Senior unsecured notes, net of debt issuance costs	$ 738,931,000	$ 737,237,000
6.000% senior unsecured notes
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	6.00%	6.00%
Principal	$ 400,000,000	$ 400,000,000
Unamortized debt issuance expense and discounts (premiums)	4,090,000	4,624,000
Senior unsecured notes, net of debt issuance costs	$ 395,910,000	$ 395,376,000
5.625% senior unsecured notes
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	5.625%	5.625%
Principal	$ 350,000,000	$ 350,000,000
Unamortized debt issuance expense and discounts (premiums)	4,372,000	4,820,000
Senior unsecured notes, net of debt issuance costs	$ 345,628,000	$ 345,180,000
6.500% senior unsecured notes
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	6.50%	6.50%
Principal	$ 550,000,000	$ 550,000,000
Unamortized debt issuance expense and discounts (premiums)	7,631,000	8,241,000
Senior unsecured notes, net of debt issuance costs	$ 542,369,000	$ 541,759,000
6.250% senior unsecured notes
Debt Instrument [Line Items]
Senior unsecured notes, stated rate	6.25%	6.25%	6.25%
Principal	$ 450,000,000	$ 450,000,000	$ 450,000,000
Unamortized debt issuance expense and discounts (premiums)	6,701,000	7,189,000
Senior unsecured notes, net of debt issuance costs	443,299,000	442,811,000
Senior Secured Credit Facility
Debt Instrument [Line Items]
Unamortized debt issuance expense and discounts (premiums)	9,200,000	10,800,000
Line of Credit
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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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.

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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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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 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.

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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.

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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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