Long-term Debt - Summary of long-term debt (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014
Debt Instrument [Line Items]
Principal amount of long-term debt	$ 1,215,078	$ 1,285,469
Less unamortized debt issuance costs	(4,866)	(5,178)
Total long-term debt	1,210,212	1,280,291
Less current portion	(41,563)	(41,563)
Long-term debt, net of current portion	1,168,649	1,238,728
Bank credit facility - Term Loan
Debt Instrument [Line Items]
Principal amount of long-term debt	800,078	810,469
Bank credit facility - Revolving Facility
Debt Instrument [Line Items]
Principal amount of long-term debt	$ 415,000	$ 475,000

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond 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, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt, after unamortized discount or premium, scheduled 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 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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