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Debt - 2014 Senior Notes (Details) - USD ($)			12 Months Ended
	Mar. 16, 2018	Oct. 06, 2014	Sep. 30, 2018	Dec. 31, 2018
The 2022 Notes
Debt
Redemption price equal to principal amount (in percent)	104.313%
Prepayment premium redemption			$ 34,500,000
2014 Senior Notes | The 2022 Notes
Debt
Principal amount		$ 800,000,000
Interest rate (as a percent)		5.75%
2014 Senior Notes | The 2024 Notes
Debt
Principal amount		$ 800,000,000
Interest rate (as a percent)		5.875%
Fair value of debt instrument				$ 788,000,000
2014 Senior Notes | The 2024 Notes | Prior to July 15 2024
Debt
Redemption price equal to principal amount (in percent)		100.00%
2014 Senior Notes | The 2024 Notes | On or after July 15, 2024
Debt
Redemption price equal to principal amount (in percent)		100.00%

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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-Publisher FASB
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