Carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Convertible Notes Payable, excluding current portion. Convertible Notes Payable is a written promise to pay a note which can be exchanged for a specified amount of another, related security, at the option of the issuer and the holder.

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

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-Section S99

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-Name Regulation S-X (SX)

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-Paragraph 22

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Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date before deducting unamortized discount or premiums (if any). May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer.

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-Article 9

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-Name FASB Staff Position (FSP)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

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-Publisher FASB

-Name Accounting Standards Codification

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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Summary of Senior Convertible Notes (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Senior convertible notes due December 15, 2013	Dec. 31, 2011 Senior convertible notes due December 15, 2013	Dec. 12, 2006 Senior convertible notes due December 15, 2013	Dec. 31, 2012 Senior convertible notes due August 15 2015	Dec. 31, 2011 Senior convertible notes due August 15 2015	Aug. 18, 2010 Senior convertible notes due August 15 2015
Debt Instrument [Line Items]
Principal amount			$ 115,000	$ 115,000	$ 115,000	$ 100,000	$ 100,000	$ 100,000
Unaccreted debt issuance expense			(557)	(1,140)		(2,417)	(3,218)
Net carrying amount			114,443	113,860		97,583	96,782
Senior convertible notes	$ 97,583	$ 210,642