Long-Term Debt - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Debt Instrument [Line Items]
Long-term debt	$ 2,900,000	$ 3,150,000	$ 2,150,000
Debt issuance costs and debt discount	(50,078)	(26,881)	(13,596)
Long-term debt	2,849,922	3,123,119	2,136,404
Less: current portion	0	(250,000)	(250,000)
Total long-term debt	2,849,922	2,873,119	1,886,404
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 2018 and March 2023 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	250,000	500,000	500,000
2014 Senior Notes due May 2019 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	0	500,000	500,000
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	$ 1,000,000	$ 0

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 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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