Long-term Debt (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Long-term Debt
Debt and Capital Lease Obligations, Total	$ 1,300,653,000us-gaap_DebtAndCapitalLeaseObligations	$ 1,261,888,000us-gaap_DebtAndCapitalLeaseObligations
Less current maturities of long-term debt	(40,890,000)	(30,853,000)
Less discount on senior secured credit facility Term Loan B	(1,014,000)	(1,056,000)
Less debt issuance costs, net of accumulated amortization of $8.3 million and $6.8 million, respectively	(23,688,000)us-gaap_UnamortizedDebtIssuanceExpense	(25,151,000)us-gaap_UnamortizedDebtIssuanceExpense
Long-term debt, net of current maturities and debt issuance costs	1,235,061,000us-gaap_LongTermDebtNoncurrent	1,204,828,000us-gaap_LongTermDebtNoncurrent
Debt issuance costs, accumulated amortization (in dollars)	8,300,000	6,800,000
Senior Secured Credit Facility
Long-term Debt
Debt and Capital Lease Obligations, Total	830,625,000	807,500,000
Senior Unsecured 5.875% Percent Notes
Long-term Debt
Debt and Capital Lease Obligations, Total	300,000,000	300,000,000
Debt instrument interest rate stated percentage	5.875%
Principal amount	300,000,000
Other long-term obligations
Long-term Debt
Debt and Capital Lease Obligations, Total	169,840,000	154,189,000
Capital leases
Long-term Debt
Debt and Capital Lease Obligations, Total	$ 188,000	$ 199,000

Carrying amount of accumulated amortization of long-term deferred finance costs capitalized at the end of the reporting period.

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Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

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

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Amount of long-term debt and capital leases due within one year or the normal operating cycle, if longer.

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Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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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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