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

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

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Long-Term Debt (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2013	Apr. 30, 2014	Feb. 28, 2015
Long-Term Debt
Long-term debt	$ 1,342,581,000us-gaap_LongTermDebtNoncurrent	$ 1,300,295,000us-gaap_LongTermDebtNoncurrent
6% senior notes due April 2021
Long-Term Debt
Long-term debt	345,677,000	345,528,000
Interest rate (as a percent)	6.00%	6.00%	6.00%
Unamortized debt issuance discount	4,300,000	4,500,000
6% senior notes due October 2022
Long-Term Debt
Long-term debt	344,904,000	344,767,000
Interest rate (as a percent)	6.00%	6.00%		6.00%
Unamortized debt issuance discount	5,100,000	5,200,000
Revolving credit facility due May 2018
Long-Term Debt
Long-term debt	502,000,000	460,000,000
Term loan facility due May 2018
Long-Term Debt
Long-term debt	$ 150,000,000	$ 150,000,000			$ 150,000,000