Long-Term Debt - Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Debt Instrument [Line Items]
Long-term debt	$ 2,900,000	$ 2,900,000	$ 2,900,000
Debt issuance costs and debt discount	(44,806)	(48,277)	(51,823)
Long-term debt	2,855,194	2,851,723	2,848,177
Less: current portion	0	0	0
Total long-term debt	2,855,194	2,851,723	2,848,177
2010 Senior Notes due October 2020 and October 2040 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	500,000	500,000	500,000
2011 Senior Notes due November 2041 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	300,000	300,000	300,000
2013 Senior Notes due March 2023 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	250,000	250,000	250,000
2016 Senior Notes due August 2021 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	350,000	350,000	350,000
2017/2018 Senior Notes due December 2025 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	$ 1,500,000	$ 1,500,000	$ 1,500,000

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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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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