Long-Term Debt And Other Long-Term Liabilities (Long-Term Debt) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total principal amount	$ 690,000	$ 650,000
Less: unamortized discount	(1,464)	(1,623)
Less: debt issuance costs, net	(3,505)	(3,902)
Total long-term debt	$ 685,031	644,475
Interest percentage of senior subordinated notes	6.625%
Debt instrument maturity date	May 15, 2021
6.625% Senior Subordinated Notes Due 2021 [Member]
Debt Instrument [Line Items]
6.625% senior subordinated notes due 2021	$ 650,000	650,000
Interest percentage of senior subordinated notes	6.625%
Debt instrument maturity date	May 15, 2021
Unit Credit Agreement [Member]
Debt Instrument [Line Items]
Credit agreement	$ 40,000	$ 0
Revolving credit facility interest rate	4.00%	0.00%
Superior Credit Agreement [Member]
Debt Instrument [Line Items]
Credit agreement	$ 0	$ 0
Revolving credit facility interest rate	0.00%	0.00%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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- Definition

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

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- Definition

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

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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.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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- Definition

Amount, after accumulated amortization, of debt discount.

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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.

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- Definition

The effective interest rate at the end of the reporting period.

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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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- 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.

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