Long-Term Debt - Summary (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Debt Instrument [Line Items]
Long-term debt	$ 2,900,000	$ 3,150,000	$ 2,150,000
Debt issuance costs and debt discount	(28,229)	(26,881)	(15,018)
Long-term debt	2,871,771	3,123,119	2,134,982
Less: current portion	0	(250,000)	(250,000)
Total long-term debt	2,871,771	2,873,119	1,884,982
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	500,000	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 Senior Notes due December 2025 \| Senior Notes
Debt Instrument [Line Items]
Long-term debt	$ 1,000,000	$ 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
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-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Publisher FASB
-Name Accounting Standards Codification
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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