Convertible Debentures and Credit Arrangements - Schedule of Convertible Senior Debentures (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Convertible senior debentures	$ 50,563us-gaap_ConvertibleDebt	$ 49,948us-gaap_ConvertibleDebt
Less: current portion	0us-gaap_ConvertibleDebtCurrent	(470)us-gaap_ConvertibleDebtCurrent
Convertible senior debentures—non-current	50,563us-gaap_ConvertibleDebtNoncurrent	49,478us-gaap_ConvertibleDebtNoncurrent
Convertible Senior Debentures due 2018 [Member]
Debt Instrument [Line Items]
Convertible senior debentures	50,563	49,478
Convertible Senior Debentures due 2024 [Member]
Debt Instrument [Line Items]
Convertible senior debentures	0	441
Convertible Senior Debentures due 2014 [Member]
Debt Instrument [Line Items]
Convertible senior debentures	$ 0	$ 29

Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 210

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-Publisher SEC

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.20)

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- Definition

Carrying amount of long-term convertible debt as of the balance sheet date, net of the amount due in the next twelve months or greater than the normal operating cycle, if longer. The debt is convertible into another form of financial instrument, typically the entity's common stock.

+ References

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)

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