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Debt - January 2012, May 2014, and November 2015 Exchangeable Senior Notes - Additional Information (Detail) - Convertible Debt - USD ($) | 1 Months Ended |  |  |
--- | --- | --- | --- | ---
Mar. 31, 2017 | Jan. 31, 2017 | Sep. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017
2012 Notes |  |  |  |  |
Debt Disclosure [Line Items] |  |  |  |  |
Convertible senior notes, stated interest rate |  | 3.50% |  |  |
Convertible senior notes, due date |  | 2032 |  |  |
Convertible senior notes, principal amount purchase |  | $ 15,000,000 |  |  |
Convertible senior notes, aggregate principal amount redeemed | $ 100,000 |  |  |  |
Convertible senior notes, outstanding amount |  |  |  |  | $ 0
2012, 2014 and 2015 Notes |  |  |  |  |
Debt Disclosure [Line Items] |  |  |  |  |
Convertible senior notes, outstanding amount |  |  | $ 0 | $ 0 |

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- Definition Debt disclosure. + References No definition available. + Details
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- Definition Debt instrument aggregate principal amount redeemed. + References No definition available. + Details
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- Definition Debt instrument maturity year. + References No definition available. + Details
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- Definition The portion of the carrying value of long-term convertible debt as of the balance sheet date that is scheduled to be repaid within one year or in the normal operating cycle if longer. Convertible debt is a financial instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(19)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Face (par) amount of the original debt instrument that was repurchased. + References No definition available. + Details
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