Convertible Senior Notes Due 2017 - Interest Expense on Convertible Notes (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Debt Disclosure [Abstract]
Coupon interest expense	$ 1,698	$ 1,698
Non-cash amortization of debt discount	3,605	3,257
Non-cash amortization of debt issuance costs	305us-gaap_AmortizationOfFinancingCosts	275us-gaap_AmortizationOfFinancingCosts
Total	$ 5,608us-gaap_InterestExpenseDebt	$ 5,230us-gaap_InterestExpenseDebt

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount of noncash expense included in interest expense to issue debt and obtain financing associated with the related debt instruments. Alternate captions include noncash interest expense.

+ References

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Represents the portion of interest incurred in the period on debt arrangements that was charged against earnings, excluding amortization of debt discount (premium) and financing costs.

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