Debt - Outstanding Convertible Note Balances (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Liability component:
Principal	$ 816,417
Long-term Debt	742,535	$ 734,683
Convertible Debt
Liability component:
Principal	341,417
Less: debt discount and issuance costs, net	65,788
Long-term Debt	275,629
Equity Component	82,481
Convertible Debt \| 2022 Convertible Notes
Liability component:
Principal	320,000
Less: debt discount and issuance costs, net	65,098
Long-term Debt	254,902	248,194
Equity Component	72,576
Convertible Debt \| 2019 Convertible Notes
Liability component:
Principal	21,417
Less: debt discount and issuance costs, net	690
Long-term Debt	20,727	$ 20,198
Equity Component	$ 9,905

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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
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- Definition

The carrying amount of the equity component of convertible debt which may be settled in cash upon conversion.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
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Amount of unamortized debt discount (premium) and debt issuance costs.

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- Definition

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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

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-SubTopic 210
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